Appendix
A. The constants which appear in the nondegenerate one-soliton solution (10a)–(10b)
The constants which appear in the nondegenerate one-soliton solution (10a)–(10b) have the explicit forms,
$$\begin{aligned}&\text{ e }^{\varDelta _1^{(j)}}=\frac{(-1)^j(\bar{k}_1^{(1)}-\bar{k}_1^{(2)})\alpha _1^{(1)}\alpha _1^{(2)}\beta _1^{(3-j)}}{(\bar{k}_1^{(j)}+k_1^{(3-j)})(k_1^{(3-j)}+\bar{k}_1^{(3-j)})^2}, \end{aligned}$$
(26)
$$\begin{aligned}&\text{ e }^{\gamma _1^{(j)}}=\frac{(-1)^j(k_1^{(1)}-k_1^{(2)})\alpha _1^{(3-j)}\beta _1^{(1)}\beta _1^{(2)}}{(k_1^{(j)}+\bar{k}_1^{(3-j)})(k_1^{(3-j)}+\bar{k}_1^{(3-j)})^2},\nonumber \\&\quad ~ j=1,2, \end{aligned}$$
(27)
$$\begin{aligned}&\text{ e }^{\delta _1}=\frac{-\alpha _1^{(1)}\beta _1^{(1)}}{(k_1^{(1)}+\bar{k}_1^{(1)})^2},~\text{ e }^{\delta _2}=\frac{-\alpha _1^{(2)}\beta _1^{(2)}}{(k_1^{(2)}+\bar{k}_1^{(2)})^2}, \end{aligned}$$
(28)
$$\begin{aligned}&\text{ e }^{\delta _3}=\frac{\alpha _1^{(1)}\alpha _1^{(2)}\beta _1^{(1)}\beta _1^{(2)}(k_1^{(1)}-k_1^{(2)})(\bar{k}_1^{(1)}-\bar{k}_1^{(2)})}{(k_1^{(1)}+\bar{k}_1^{(1)})^2(\bar{k}_1^{(1)}+k_1^{(2)})(k_1^{(1)}+\bar{k}_1^{(2)})(k_1^{(2)}+\bar{k}_1^{(2)})^2}.\nonumber \\ \end{aligned}$$
(29)
B. The constants which appear in the reduced form of general two-soliton solution (21a)–(21b)
The following constants appear in the two-soliton solution (21a)–(21b)
$$\begin{aligned} \text{ e }^{\varDelta _1^{(j)}}= & {} \bar{\varrho }_{12}(-1)^{3-j}k_1\beta _1^{(3-j)}\nu _1+\bar{k}_2\alpha _2^{(j)}\varGamma _{11}\\&-\,\bar{k}_1\alpha _1^{(j)}\varGamma _{21}]/\kappa _{11}\kappa _{12}, \end{aligned}$$
$$\begin{aligned} \text{ e }^{\varDelta _2^{(j)}}= & {} \bar{\varrho }_{12}[(-1)^{3-j}k_2\beta _2^{(3-j)}\nu _1+\bar{k}_2\alpha _2^{(j)}\varGamma _{12}\\&-\,\bar{k}_1\alpha _1^{(j)}\varGamma _{22}]/\kappa _{21}\kappa _{22},\\ \text{ e }^{\gamma _1^{(j)}}= & {} \varrho _{12}[k_2\beta _2^{(j)}\varGamma _{11}-k_1\beta _1^{(j)}\varGamma _{12}\\&+\,(-1)^{(j)}\bar{k}_1\alpha _1^{(3-j)}\nu _2]/\kappa _{11}\kappa _{21},\\ \text{ e }^{\gamma _2^{(j)}}= & {} \varrho _{12}[k_2\beta _2^{(j)}\varGamma _{21}-k_1\beta _1^{(j)}\varGamma _{22}\\&+\,(-1)^{(j)}\bar{k}_2\alpha _2^{(3-j)}\nu _2]/\kappa _{12}\kappa _{22},\\ \text{ e }^{\delta _{1}}= & {} -\frac{\varGamma _{11}}{\kappa _{11}},~\text{ e }^{\delta _{2}}=-\frac{\varGamma _{21}}{\kappa _{12}},\\ ~\text{ e }^{\delta _{3}}= & {} -\frac{\varGamma _{12}}{\kappa _{21}},~\text{ e }^{\delta _{4}}=-\frac{\varGamma _{22}}{\kappa _{22}}, \\ \text{ e }^{\delta _{5}}= & {} \varrho _{12}\bar{\varrho }_{12}(\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2\\&-\,\varrho _{3}\varGamma _{21}\varGamma _{12})/\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}. \end{aligned}$$
Correspondingly in the \(\mathscr {PT}\)-symmetry preserving two-soliton solution (23), the form of various constants can be given as follows.
$$\begin{aligned} \text{ e }^{\delta _1}= & {} \frac{2(l_1+\bar{l}_2)(l_2+\bar{l}_1)}{(l_1-l_2)(\bar{l}_1-\bar{l}_2)}\text{ e }^{i(\theta _{12}+\varphi _{12})},\\ \text{ e }^{\delta _2}= & {} \frac{-2(l_1+\bar{l}_1)(l_2+\bar{l}_2)}{(l_1-l_2)(\bar{l}_1-\bar{l}_2)}\text{ e }^{i(\theta _{22}+\varphi _{12})},\\ \text{ e }^{\delta _3}= & {} \frac{-2(l_1+\bar{l}_1)(l_2+\bar{l}_2)}{(l_1-l_2)(\bar{l}_1-\bar{l}_2)}\text{ e }^{i(\theta _{12}+\varphi _{22})},\\ \text{ e }^{\delta _4}= & {} \frac{2(l_1+\bar{l}_2)(l_2+\bar{l}_1)}{(l_1-l_2)(\bar{l}_1-\bar{l}_2)}\text{ e }^{i(\theta _{22}+\varphi _{22})},\\ \text{ e }^{\varDelta _1^{(j)}}= & {} -\frac{2(l_1+\bar{l}_2)(l_2+\bar{l}_2)}{(\bar{l}_1-\bar{l}_2)}\text{ e }^{i(\theta _{12}+\varphi _{12}+\theta _{2j})},\\ \text{ e }^{\delta _5}= & {} 4\text{ e }^{i(\theta _{12}+\theta _{22}+\varphi _{12}+\varphi _{22})},\\ \text{ e }^{\varDelta _2^{(j)}}= & {} \frac{2(l_1+\bar{l}_1)(l_2+\bar{l}_1)}{(\bar{l}_1-\bar{l}_2)}\text{ e }^{i(\theta _{12}+\varphi _{22}+\theta _{2j})}, ~j=1,2. \end{aligned}$$
C. The unfactored degenerate two-soliton solution
A general unfactored degenerate two-soliton solution can be deduced by considering the following forms of seed solution for the functions \(g_1^{(j)}(x,t)\) and \(g_1^{(j)*}(-x,t)\), for Eq. (8) that is
$$\begin{aligned}&g^{(j)}_1(x,t)=\alpha _{1}^{(j)}\text{ e }^{\bar{\xi }_1}+\alpha _{2}^{(j)}\text{ e }^{\bar{\xi }_2},~\bar{\xi _j}=i \bar{k_{j}}x+i\bar{k_{j}^{2}}t , \end{aligned}$$
(30a)
$$\begin{aligned}&g^{(j)*}_1(-x,t)=\beta _{1}^{(j)}\text{ e }^{\xi _1}+\beta _{2}^{(j)}\text{ e }^{\xi _2},\nonumber \\&\quad \xi _{j}=i k_{j}x-ik_{j}^{2}t, ~j=1,2 . \end{aligned}$$
(30b)
The above form of seed solutions truncates the series expansions (7a)–(7c) at in 7-th order in \(g^{(j)}(x,t)\) and \(g^{(j)*}(-x,t)\), at 8-th order in f(x, t) and \(f^{*}(-x,t)\) and 6-th order in \(s^{(1)}(-x,t)\) and \(s^{(2)}(-x,t)\). By solving the resultant equations that arise at each order of \(\epsilon \), we have obtained the following expressions for the unknown functions \(g^{(j)}(x,t)\), \(g^{(j)*}(-x,t)\) and f(x, t),
$$\begin{aligned} g^{(j)}(x,t)= & {} \alpha _{1}^{(j)}\text{ e }^{\bar{\xi }_1}+\alpha _{2}^{(j)}\text{ e }^{\bar{\xi }_2}+\text{ e }^{\xi _{1}+2\bar{\xi }_1+\varDelta _{1}^{(j)}}\nonumber \\&+\,\text{ e }^{\xi _{2}+2\bar{\xi _1}+\varDelta _{2}^{(j)}}+\text{ e }^{\xi _{1}+2\bar{\xi _2}+\varDelta _{3}^{(j)}}\nonumber \\&+\,\text{ e }^{\xi _{2}+2\bar{\xi _2}+\varDelta _{4}^{(j)}} +\text{ e }^{\xi _{1}+\bar{\xi _1}+\bar{\xi _2}+\varDelta _{5}^{(j)}}\nonumber \\&+\,\text{ e }^{\xi _{2}+\bar{\xi _1}+\bar{\xi _2}+\varDelta _{6}^{(j)}}+\text{ e }^{2\xi _{1}+2\bar{\xi _1}+\bar{\xi _2}+\,\varDelta _{7}^{(j)}}\nonumber \\&+\,\text{ e }^{2\xi _{1}+\bar{\xi _1}+2\bar{\xi _2}+\varDelta _{8}^{(j)}}+\text{ e }^{2\xi _{2}+2\bar{\xi _1}+\bar{\xi _2}+\varDelta _{9}^{(j)}}\nonumber \\&+\,\text{ e }^{2\xi _{2}+\bar{\xi _1}+2\bar{\xi _2}+\mu _{1}^{(j)}}+\text{ e }^{\xi _{1}+\bar{\xi _1}+\xi _2+2\bar{\xi _2}+\mu _{2}^{(j)}}\nonumber \\&+\,\text{ e }^{\xi _{1}+2\bar{\xi _1}+\xi _2+\bar{\xi _2}+\mu _{3}^{(j)}}\nonumber \\&+\,\text{ e }^{2\xi _{1}+2\bar{\xi _1}+\xi _{2}+2\bar{\xi _2}+\mu _{4}^{(j)}}\nonumber \\&+\,\text{ e }^{2\bar{\xi _1}+2\bar{\xi _2}+\xi _{1}+2\xi _{2}+\mu _{5}^{(j)}}\end{aligned}$$
(31a)
$$\begin{aligned} g^{(j)*}(-x,t)= & {} \beta _{1}^{(j)}\text{ e }^{\xi _{1}}+\beta _{2}^{(j)}\text{ e }^{\xi _{2}}+\text{ e }^{2\xi _{1}+\bar{\xi _1}+\gamma _{1}^{(j)}}\nonumber \\&+\,\text{ e }^{2\xi _{1}+\bar{\xi _2}+\gamma _{2}^{(j)}}+\text{ e }^{2\xi _{2}+\bar{\xi _1}+\gamma _{3}^{(j)}}\nonumber \\&+\,\text{ e }^{2\xi _{2}+\bar{\xi _2}+\gamma _{4}^{(j)}}+\text{ e }^{\xi _{1}+\bar{\xi _1}+\xi _{2}+\gamma _{5}^{(j)}}\nonumber \\&+\,\text{ e }^{\xi _{1}+\xi _{2}+\bar{\xi _2}+\gamma _{6}^{(j)}}+\text{ e }^{2\xi _{1}+2\bar{\xi _1}+\xi _{2}+\gamma _{7}^{(j)}}\nonumber \\&+\,\text{ e }^{\xi _{1}+2\bar{\xi _1}+2\xi _{2}+\gamma _{8}^{(j)}}+\text{ e }^{2\xi _{1}+2\bar{\xi _2}+\xi _{2}+\gamma _{9}^{(j)}}\nonumber \\&+\,\text{ e }^{2\xi _{2}+2\bar{\xi _2}+\xi _{1}+\varphi _{1}^{(j)}}+\text{ e }^{2\xi _{1}+\bar{\xi _1}+\xi _{2}+\bar{\xi _2}+\varphi _{2}^{(j)}}\nonumber \\&+\,\text{ e }^{\xi _{1}+\bar{\xi _1}+2\xi _{2}+\bar{\xi _2}+\varphi _{3}^{(j)}}\nonumber \\&+\,\text{ e }^{2\xi _{1}+2\bar{\xi _1}+2\xi _{2}+\bar{\xi _2}+\varphi _{4}^{(j)}}\nonumber \\&+\,\text{ e }^{2\xi _{1}+\bar{\xi _1}+2\xi _{2}+2\bar{\xi _2}+\varphi _{5}^{(j)}}\end{aligned}$$
(31b)
$$\begin{aligned} f(x,t)= & {} 1+\text{ e }^{\xi _{1}+\bar{\xi _1}+\delta _1}+\text{ e }^{\xi _{2}+\bar{\xi _1}+\delta _2}+\text{ e }^{\xi _{1}+\bar{\xi _2}+\delta _3}\nonumber \\&+\,\text{ e }^{\xi _{2}+\bar{\xi _2}+\delta _4}+\text{ e }^{2(\xi _{1}+\bar{\xi _1})+\delta _{11}}\nonumber \\&+\,\text{ e }^{2(\xi _{2}+\bar{\xi _1})+\delta _{12}}+\text{ e }^{2(\xi _{1}+\bar{\xi _2})+\delta _{13}}\nonumber \\&+\,\text{ e }^{2(\xi _{2}+\bar{\xi _2})+\delta _{14}}+\text{ e }^{2\bar{\xi _1}+\xi _{1}+\xi _{2}+\delta _{15}}\nonumber \\&+\,\text{ e }^{2\bar{\xi _2}+\xi _{1}+\xi _{2}+\delta _{16}}+\text{ e }^{2\xi _{1}+\bar{\xi _1}+\bar{\xi _2}+\delta _{17}}\nonumber \\&+\,\text{ e }^{2\xi _{2}+\bar{\xi _1}+\bar{\xi _2}+\delta _{18}}+\text{ e }^{\xi _{1}+\bar{\xi _1}+\xi _{2}+\bar{\xi _2}+\delta _{19}}\nonumber \\&+\,\text{ e }^{2\xi _{1}+2\bar{\xi _1}+\xi _{2}+\bar{\xi _2}+\delta _{21}}\nonumber \\&+\,\text{ e }^{2\xi _{1}+\bar{\xi _1}+\xi _{2}+2\bar{\xi _2}+\delta _{22}}\nonumber \\&+\,\text{ e }^{\xi _{1}+2\bar{\xi _1}+2\xi _{2}+\bar{\xi _2}+\delta _{23}}\nonumber \\&+\,\text{ e }^{\xi _{1}+\bar{\xi _1}+2\xi _{2}+2\bar{\xi _2}+\delta _{24}}\nonumber \\&+\,\text{ e }^{2(\xi _{1}+\bar{\xi _1}+\xi _{2}+\bar{\xi _2})+\delta _{31}}\equiv f^{*}(-x,t). \nonumber \\ \end{aligned}$$
(31c)
The explicit expression of all the constants that appear in two-soliton solution is given as
$$\begin{aligned} \text{ e }^{\delta _{1}}= & {} -2\frac{\varGamma _{11}}{\kappa _{11}},~\text{ e }^{\delta _{2}}=-2\frac{\varGamma _{12}}{\kappa _{21}},\\&\text{ e }^{\delta _{3}}=-2\frac{\varGamma _{21}}{\kappa _{12}},~\text{ e }^{\delta _{4}}=-2\frac{\varGamma _{22}}{\kappa _{22}},\\ \varGamma _{11}= & {} \left( \alpha ^{(1)}_1\beta ^{(1)}_1+\alpha ^{(2)}_1\beta ^{(2)}_1\right) ,\\ \varGamma _{12}= & {} \left( \alpha ^{(1)}_1\beta ^{(1)}_2+\alpha ^{(2)}_1\beta ^{(2)}_2\right) ,\\ \varGamma _{21}= & {} \left( \alpha ^{(1)}_2\beta ^{(1)}_1+\alpha ^{(2)}_2\beta ^{(2)}_1\right) ,\\ \varGamma _{22}= & {} \left( \alpha ^{(1)}_2\beta ^{(1)}_2+\alpha ^{(2)}_2\beta ^{(2)}_2\right) ,\\ \kappa _{lm}= & {} (k_l+\bar{k}_m)^2 ,~l,m=1,2.\\ \text{ e }^{\varDelta _{1}^{(j)}}= & {} -\frac{\alpha _1^{(j)}\varGamma _{11}}{\kappa _{11}},~\text{ e }^{\varDelta _{2}^{(j)}}=-\frac{\alpha _1^{(j)}\varGamma _{12}}{\kappa _{21}},\\ \text{ e }^{\varDelta _{3}^{(j)}}= & {} -\frac{\alpha _2^{(j)}\varGamma _{21}}{\kappa _{12}},~\text{ e }^{\varDelta _{4}^{(j)}}=-\frac{\alpha _2^{(j)}\varGamma _{22}}{\kappa _{22}}, \\ \text{ e }^{\varDelta _{5}^{(j)}}= & {} -\bigg (\alpha _1^{(j)}\varGamma _{21}(k_1+\bar{k}_1)(k_1+2\bar{k}_1-\bar{k}_2)\\&+\,\alpha _2^{(j)}\varGamma _{11}(k_1+\bar{k}_2)(k_1+2\bar{k}_2-\bar{k}_1)\bigg )/\kappa _{11}\kappa _{12},~\\ \text{ e }^{\varDelta _{6}^{(j)}}= & {} -\bigg (\alpha _1^{(j)}\varGamma _{22}(k_2+\bar{k}_1)(k_2+2\bar{k}_1-\bar{k}_2)\\&+\,\alpha _2^{(j)}\varGamma _{12}(k_2+\bar{k}_2)(k_2+2\bar{k}_2-\bar{k}_1)\bigg )/ \kappa _{21}\kappa _{22},\\ \text{ e }^{\gamma _{1}^{(j)}}= & {} -\frac{\beta _1^{(j)}\varGamma _{11}}{\kappa _{11}},~\text{ e }^{\gamma _{2}^{(j)}}=-\frac{\beta _1^{(j)}\varGamma _{21}}{\kappa _{12}},\\ \text{ e }^{\gamma _{3}^{(j)}}= & {} -\frac{\beta _2^{(j)}\varGamma _{12}}{\kappa _{21}},~\text{ e }^{\gamma _{4}^{(j)}}=-\frac{\beta _2^{(j)}\varGamma _{22}}{\kappa _{22}},\\ \text{ e }^{\gamma _{5}^{(j)}}= & {} -\bigg (\beta _1^{(j)}\varGamma _{12}(k_1+\bar{k}_1)(\bar{k}_1+2k_1-k_2)\\&+\,\beta _2^{(j)}\varGamma _{11}(k_2+\bar{k}_1)(\bar{k}_1+2k_2-k_1)\bigg )/\kappa _{11}\kappa _{21},\\ \text{ e }^{\gamma _{6}^{(j)}}= & {} -\bigg (\beta _1^{(j)}\varGamma _{22}(k_1+\bar{k}_2)(\bar{k}_2+2k_1-k_2)\\&+\,\beta _2^{(j)}\varGamma _{21}(k_2+\bar{k}_2)(\bar{k}_2+2k_2-k_1)\bigg )/\kappa _{12}\kappa _{22}. \end{aligned}$$
$$\begin{aligned} \text{ e }^{\delta _{11}}= & {} \frac{\varGamma _{11}^2}{\kappa _{11}^2},~\text{ e }^{\delta _{12}}=\frac{\varGamma _{12}^2}{\kappa _{21}^2},~\text{ e }^{\delta _{13}}=\frac{\varGamma _{21}^2}{\kappa _{12}^2},\\ \text{ e }^{\delta _{14}}= & {} \frac{\varGamma _{22}^2}{\kappa _{22}^2},~\text{ e }^{\delta _{15}}=\frac{2\varGamma _{11}\varGamma _{12}}{\kappa _{11}\kappa _{21}},\\ \text{ e }^{\delta _{16}}= & {} \frac{2\varGamma _{21}\varGamma _{22}}{\kappa _{12}\kappa _{22}},~\text{ e }^{\delta _{17}}=\frac{2\varGamma _{11}\varGamma _{21}}{\kappa _{11}\kappa _{12}},~\text{ e }^{\delta _{18}}=\frac{2\varGamma _{12}\varGamma _{22}}{\kappa _{21}\kappa _{22}},\\ \text{ e }^{\delta _{19}}= & {} \frac{2(\kappa _{21}\kappa _{12})^{\frac{1}{2}}\varLambda _3+2(\kappa _{11}\kappa _{22})^{\frac{1}{2}}\varLambda _4+4\varLambda _5}{\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}},\\ \varLambda _3= & {} (k_1(2\bar{k}_1+k_2-\bar{k}_2)+2k_2\bar{k}_2+\bar{k}_1(\bar{k}_2-k_2))\\&(\alpha _1^{(1)}\beta _1^{(1)}\alpha _2^{(2)}\beta _2^{(2)}+\alpha _1^{(1)}\beta _1^{(2)}\alpha _2^{(1)}\beta _2^{(1)}),\\ \varLambda _4= & {} (-k_2\bar{k}_2+\bar{k}_1(2k_2+\bar{k}_2)+k_1(2\bar{k}_2-\bar{k}_1+k_2))\\&(\alpha _1^{(2)}\beta _1^{(1)}\alpha _2^{(1)}\beta _2^{(2)}+\alpha _1^{(1)}\beta _1^{(2)}\alpha _2^{(2)}\beta _2^{(1)}),\\ \varLambda _5= & {} (k_2^2\bar{k}_2^2+k_2\bar{k}_1\bar{k}_2(\bar{k}_2-k_2)\\&+\,\bar{k}_1^2(k_2^2+k_2\bar{k}_2+\bar{k}_2^2)+k_1^2(\bar{k}_1^2+k_2^2\\&+\,\bar{k}_1(k_2-\bar{k}_2)+k_2\bar{k}_2\\&+\,\bar{k}_2^2)+k_1[k_2\bar{k}_2(k_2-\bar{k}_2)+\bar{k}_1^2(\bar{k}_2-k_2)\\&+\,\bar{k}_1(k_2^2+5k_2\bar{k}_2+\bar{k}_2^2)])\\&(\alpha _1^{(2)}\beta _1^{(2)}\alpha _2^{(2)}\beta _2^{(2)}+\alpha _1^{(1)}\beta _1^{(1)}\alpha _2^{(1)}\beta _2^{(1)}).\\ \text{ e }^{\varDelta _{7}^{(j)}}= & {} \bar{\varrho }_{12}\varGamma _{11}\bigg ((-1)^{j}k_1\beta _1^{(3-j)}\nu _1\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{11}+\bar{k}_1\alpha _1^{(j)}\varGamma _{21}\bigg )/\kappa _{11}^2\kappa _{12},\\ \text{ e }^{\varDelta _{8}^{(j)}}= & {} \bar{\varrho }_{12}\varGamma _{21}\bigg ((-1)^{j}k_1\beta _1^{(3-j)}\nu _1\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{11}+\bar{k}_1\alpha _1^{(j)}\varGamma _{21}\bigg )/\kappa _{11}\kappa _{12}^2,\\ \text{ e }^{\varDelta _{9}^{(j)}}= & {} \bar{\varrho }_{12}\varGamma _{12}\bigg ((-1)^{j}k_2\beta _2^{(3-j)}\nu _1\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{12}+\bar{k}_1\alpha _1^{(j)}\varGamma _{22}\bigg )/\kappa _{21}^2\kappa _{22},\\ \text{ e }^{\mu _{1}^{(j)}}= & {} \bar{\varrho }_{12}\varGamma _{22}\bigg ((-1)^{j}k_2\beta _2^{(3-j)}\nu _1\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{12}+\bar{k}_1\alpha _1^{(j)}\varGamma _{22}\bigg )/\kappa _{21}\kappa _{22}^2,\\ \end{aligned}$$
$$\begin{aligned} \text{ e }^{\gamma _{7}^{(j)}}= & {} \varrho _{12}\varGamma _{11}\bigg (-k_2\beta _2^{(j)}\varGamma _{11}\\&+\,k_1\beta _1^{(j)}\varGamma _{12}+(-1)^{(3-j)}\bar{k}_1\alpha _1^{(3-j)}\nu _2\bigg )/\kappa _{11}^2\kappa _{21},\\ \text{ e }^{\gamma _{8}^{(j)}}= & {} \varrho _{12}\varGamma _{12}\bigg (-k_2\beta _2^{(j)}\varGamma _{11}\\&+\,k_1\beta _1^{(j)}\varGamma _{12}+(-1)^{(3-j)}\bar{k}_1\alpha _1^{(3-j)}\nu _2\bigg )/\kappa _{11}\kappa _{21}^2,\\ \text{ e }^{\gamma _{9}^{(j)}}= & {} \varrho _{12}\varGamma _{21}\bigg (-k_2\beta _2^{(j)}\varGamma _{21}\\&+\,k_1\beta _1^{(j)}\varGamma _{22}+(-1)^{(3-j)}\bar{k}_2\alpha _2^{(3-j)}\nu _2\bigg )/\kappa _{12}^2\kappa _{22},\\ \text{ e }^{\varphi _{1}^{(j)}}= & {} \varrho _{12}\varGamma _{22}\bigg (-k_2\beta _2^{(j)}\varGamma _{21}\\&+\,k_1\beta _1^{(j)}\varGamma _{22}+(-1)^{(3-j)}\bar{k}_2\alpha _2^{(3-j)}\nu _2\bigg )/\kappa _{12}\kappa _{22}^2,\\ \text{ e }^{\mu _2^{(j)}}= & {} \frac{\bar{\varrho }_{12}\varLambda _6}{\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}},~\text{ e }^{\mu _3^{(j)}}=\frac{\bar{\varrho }_{12}\varLambda _7}{\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}},\\ \text{ e }^{\varphi _2^{(j)}}= & {} \frac{\varrho _{12}\varLambda _8}{\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}},~ \text{ e }^{\varphi _3^{(j)}}=\frac{\varrho _{12}\varLambda _9}{\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}},\\ \varLambda _6= & {} \left( -2k_2^2\bar{k}_2\alpha _2^{(j)}\varGamma _{11}\varGamma _{22}+2\bar{k}_1^3\alpha _1^{(j)}\varGamma _{21}\varGamma _{22}\right. \\&+\,k_1^2\left[ -2\bar{k}_2\alpha _2^{(j)}\varGamma _{21}\varGamma _{12}+\bar{k}_1(\alpha _2^{(j)}\varGamma _{11}\right. \\&+\,\alpha _1^{(j)}\varGamma _{21})\varGamma _{22}+k_2\nu _1(-\alpha _2^{(j)}\nu _2\\&\left. +\beta _2^{(3-j)}(-1)^j\varGamma _{21})\right] +\bar{k}_1k_2[k_2\varGamma _{21}(\alpha _1^{(j)}\varGamma _{22}+\alpha _2^{(j)}\\&\varGamma _{12})+\bar{k}_2\alpha _2^{(j)}(\alpha _1^{(1)}(-2\beta _1^{(1)}\varGamma _{22}-\alpha _2^{(2)}\nu _2)\\&+\,\alpha _1^{(2)}(-2\beta _1^{(2)}\varGamma _{22}+\alpha _2^{(1)}\nu _2))]\\&+\,\bar{k}_1^2[k_2\varGamma _{21}(2\alpha _1^{(j)}\varGamma _{22}+(-1)^j\beta _2^{(3-j)}\nu _1)\\&-\,\bar{k}_2\alpha _2^{(j)}(\alpha _1^{(1)}(\beta _2^{(1)}\varGamma _{21}+\beta _1^{(1)}\varGamma _{22})+\alpha _1^{(2)}\\&(\beta _1^{(2)}\varGamma _{22}+\beta _2^{(2)}\varGamma _{21}))]+k_1\left[ \bar{k}_1^2\varGamma _{22}(2\alpha _1^{(j)}\varGamma _{21}\right. \\&+\,(-1)^j\beta _1^{(3-j)}\nu _1)+k_2(k_2\nu _1(-1)^j((-1)^j\\&\alpha _2^{(j)}\nu _2+\beta _1^{(3-j)}\varGamma _{22})+\bar{k}_2\alpha _2^{(j)}(\varGamma _{11}\varGamma _{22}+\varGamma _{21}\varGamma _{12}))\\&+\,\bar{k}_1\left[ \bar{k}_2\alpha _2^{(j)}\big (\alpha _1^{(1)}(-2\beta _2^{(1)}\varGamma _{21}\right. \\&+\,\alpha _2^{(2)}\nu _2)+\alpha _1^{(2)}(-\alpha _2^{(1)}\nu _2-2\beta _2^{(2)}\varGamma _{21})\big )\\&+\,k_2\big (-3\alpha _1^{(3-j)}\alpha _2^{(j)}(\beta _2^{(3-j)}\varGamma _{21}+\beta _1^{(3-j)}\varGamma _{22})\\&+\,\alpha _1^{(j)}\big (\alpha _2^{(3-j)}\beta _1^{(3-j)}\varGamma _{22}+\alpha _2^{(3-j)}\beta _2^{(3-j)}\varGamma _{21}\\&\left. \left. \left. +2\alpha _2^{(j)2}\beta _1^{(3-j)}\beta _2^{(3-j)}-2\alpha _2^{(j)2}\beta _1^{(j)}\beta _2^{(j)}\big )\big )\right] \right] \right) , \end{aligned}$$
$$\begin{aligned} \varLambda _7= & {} \bigg (-k_2\varGamma _{11}[2\bar{k}_2^2\alpha _2^{(j)}\varGamma _{12}+k_2\bar{k}_2(2\alpha _2^{(j)}\varGamma _{12}\\&+\,(-1)^{(3-j)}\beta _2^{(3-j)}\nu _1)+k_2^2(\alpha _1^{(j)}\varGamma _{22}+\alpha _2^{(j)}\\&\varGamma _{12})]+k_1^2[-\bar{k}_2(\alpha _1^{(j)}\varGamma _{21}+\alpha _2^{(j)}\varGamma _{11})\varGamma _{12}\\&+\,2\bar{k}_1\alpha _1^{(j)}\varGamma _{11}\varGamma _{22}+(-1)^jk_2\nu _1((-1)^{(3-j)}\alpha _1^{(j)}\\&\nu _2+\beta _2^{(3-j)}\varGamma _{11})]+\bar{k}_1\alpha _1^{(j)}[2k_2^2\varGamma _{21}\varGamma _{12}\\&+\,\bar{k}_2^2\big (\alpha _1^{(1)}(\beta _2^{(1)}\varGamma _{21}+\beta _1^{(1)}\varGamma _{22})+\alpha _1^{(2)}(\beta _1^{(2)}\varGamma _{22}\\&+\,\beta _2^{(2)}\varGamma _{21})\big )+k_2\bar{k}_2\big (\alpha _1^{(1)}(2\beta _2^{(1)}\varGamma _{21}-\alpha _2^{(2)}\nu _2)\\&+\,\alpha _1^{(2)}(2\beta _2^{(2)}\varGamma _{21}+\alpha _2^{(1)}\nu _2)\big )]-k_1\\&[\bar{k}_2^2(2\alpha _2^{(j)}\varGamma _{11}+(-1)^{(3-j)}\beta _1^{(3-j)}\nu _1)\varGamma _{12}\\&+\,(-1)^{(3-j)}k_2^2\nu _1((-1)^j\alpha _1^{(j)}\nu _2+\beta _1^{(3-j)}\varGamma _{12})\\&+\,k_2\bar{k}_2\big ((-1)^{(3-j)}\beta _1^{(3-j)}\varGamma _{12}\nu _1\\&+\,(-1)^{(3-j)}\beta _2^{(3-j)}\varGamma _{11}\nu _1-2\alpha _1^{(j)}\alpha _2^{(3-j)}(\beta _1^{(3-j)}\\&\varGamma _{12}+\beta _2^{(3-j)}\varGamma _{11})+2\alpha _1^{(3-j)2}\alpha _2^{(j)}\beta _1^{(3-j)}\beta _{2}^{(3-j)}\\&-\,2\alpha _1^{(j)2}\alpha _2^{(j)}\beta _1^{(j)}\beta _2^{(j)}\big )+\bar{k}_1\alpha _1^{(j)}\big (\bar{k}_2\\&(-2\varGamma _{11}\varGamma _{22}+\nu _1\nu _2)+k_2(\varGamma _{11}\varGamma _{22}+\varGamma _{12}\varGamma _{21})\big )]\bigg ),\\ \varLambda _8= & {} \bigg (-\bar{k}_1^2[\bar{k}_2(\beta _1^{(j)}\nu _1+(-1)^j\alpha _2^{(3-j)}\varGamma _{11})\nu _2\\&+\,k_2\varGamma _{21}(\beta _2^{(j)}\varGamma _{11}+\beta _1^{(j)}\varGamma _{12})]-k_2\varGamma _{11}\\&[2k_2^2\varGamma _{21}\beta _2^{(j)}+\bar{k}_2^2(\beta _2^{(j)}\varGamma _{21}+\beta _1^{(j)}\varGamma _{22})\\&+\,k_2\bar{k}_2(2\beta _2^{(j)}\varGamma _{21}+(-1)^j\alpha _2^{(3-j)}\nu _2)]\\&+\,k_1\beta _1^{(j)}[2\bar{k}_2^2\varGamma _{12}\varGamma _{21}+2\bar{k}_1^2\varGamma _{11}\varGamma _{22}\\&+\,k_2\bar{k}_2(2\varGamma _{21}\varGamma _{12}+\nu _1\nu _2)+k_2^2(\varGamma _{12}\varGamma _{21}+\varGamma _{11}\varGamma _{22})\\&+\,\bar{k}_1\big (-\bar{k}_2(\varGamma _{12}\varGamma _{21}+\varGamma _{11}\varGamma _{22})\\&+\,k_2(2\varGamma _{11}\varGamma _{22}-\nu _2\nu _2)\big )]+\bar{k}_1[(-1)^{(3-j)}\bar{k}_2^2\nu _2\\&((-1)^{(3-j)}\beta _1^{(j)}\nu _1+\alpha _1^{(3-j)}\varGamma _{21})-k_2^2\varGamma _{21}(2\beta _2^{(j)}\\ \end{aligned}$$
$$\begin{aligned}&\varGamma _{11}+(-1)^{(j)}\alpha _1^{(3-j)}\nu _2)+k_2\bar{k}_2\\&\big (\alpha _1^{(j)}\beta _1^{(j)}(2\beta _1^{(j)}\varGamma _{22}+(-1)^{(3-j)}\alpha _2^{(3-j)}\nu _2)\\&+\alpha _1^{(3-j)}((-1)^{(3-j)}\varGamma _{21}\nu _2+2\beta _1^{(j)}\beta _2^{(3-j)}\\&\varGamma _{21}+3(-1)^{(3-j)}\alpha _2^{(3-j)}\beta _1^{(3-j)}\nu _2)\big )]\bigg ),\\ \varLambda _9= & {} \bigg (-2k_2\bar{k}_2^2\varGamma _{11}\varGamma _{22}\beta _2^{(j)}+2k_1^3\beta _1^{(j)}\varGamma _{12}\varGamma _{22}\\&+\,\bar{k}_1^2(-1)^j[(-1)^{(3-j)}2k_2\varGamma _{21}\beta _2^{(j)}+(-1)^{(3-j)}\\&\bar{k}_2\nu _2(\nu _1\beta _2^{(j)}+(-1)^{(j)}\alpha _2^{(3-j)}\varGamma _{12})]\\&+\,k_1^2[\bar{k}_1\varGamma _{22}(2\beta _1^{(j)}\varGamma _{12}+(-1)^{(3-j)}\alpha _1^{(3-j)}\nu _2)\\&+\,\bar{k}_2\varGamma _{12}(2\beta _1^{(j)}\varGamma _{22}+(-1)^{(3-j)}\alpha _2^{(3-j)}\nu _2)\\&-\,k_2\beta _2^{(j)}(\varGamma _{11}\varGamma _{22}+\varGamma _{12}\varGamma _{21})]+\bar{k}_1\bar{k}_2[(-1)^{(3-j)}\bar{k}_2\\&\nu _2(\alpha _1^{(3-j)}\varGamma _{22}+(-1)^{(3-j)}\beta _2^{(j)}\nu _1)\\&+\,k_2\beta _2^{(j)}\big (\alpha _1^{(1)}(\beta _2^{(1)}\varGamma _{21}+\beta _1^{(1)}\varGamma _{22})+\alpha _1^{(2)}\\&(\beta _1^{(2)}\varGamma _{22}+\beta _2^{(2)}\varGamma _{21})\big )]\\&+\,k_1[\bar{k}_1^2\varGamma _{22}(\beta _2^{(j)}\varGamma _{11}+\beta _1^{(j)}\varGamma _{12})\\&+\,\bar{k}_2\big (\bar{k}_2\varGamma _{12}(\beta _1^{(j)}\varGamma _{22}+\beta _2^{(j)}\varGamma _{21})+k_2\beta _2^{(j)}\\&(-2\varGamma _{11}\varGamma _{22}+\nu _1\nu _2)\big )\\&+\,\bar{k}_1\big (k_2\beta _2^{(j)}[\alpha _1^{(1)}(-2\beta _2^{(1)}\varGamma _{21}+\alpha _2^{(2)}\nu _2)\\&+\,(-2\beta _2^{(2)}\varGamma _{21}-\alpha _2^{(1)}\nu _2)]\\&+\,\bar{k}_2[\alpha _1^{(j)}\beta _2^{(j)}(-2\beta _2^{(j)}\varGamma _{21}+(-1)^{(3-j)}\alpha _2^{(3-j)}\nu _2)\\&+\,\alpha _1^{(3-j)}(-2\beta _1^{(j)}\beta _2^{(j)}\varGamma _{22}+(-1)^{(3-j)}\nu _2\\&\varGamma _{22}+3(-1)^{(3-j)}\alpha _2^{(3-j)}\beta _2^{(j)}\nu _2)]\big )]\bigg ),\\ \nu _1= & {} \alpha _1^{(2)}\alpha _2^{(1)}-\alpha _1^{(1)}\alpha _2^{(2)},~\nu _2=\beta _1^{(1)}\beta _2^{(2)}-\beta _1^{(2)}\beta _2^{(1)},\\ \varrho _{12}= & {} (k_1-k_2),~\bar{\varrho }_{12}=(\bar{k}_1-\bar{k}_2), \\ \text{ e }^{\delta _{21}}= & {} -2\varrho _{12}\bar{\varrho }_{12}\varGamma _{11}\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2\\&-\,\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )/\kappa _{11}^2\kappa _{12}\kappa _{21}\kappa _{22},\\ \text{ e }^{\delta _{22}}= & {} -2\varrho _{12}\bar{\varrho }_{12}\varGamma _{21}\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2\\&-\,\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )/\kappa _{11}\kappa _{12}^2\kappa _{21}\kappa _{22}, \end{aligned}$$
$$\begin{aligned} \text{ e }^{\delta _{23}}= & {} -\,2\varrho _{12}\bar{\varrho }_{12}\varGamma _{12}\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2\\&-\,\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )/\kappa _{11}\kappa _{12}\kappa _{21}^2\kappa _{22},\\ \text{ e }^{\delta _{24}}= & {} -\,2\varrho _{12}\bar{\varrho }_{12}\varGamma _{22}\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2\\&-\,\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )/\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}^2,\\ \varrho _{1}= & {} (k_2\bar{k}_2+k_1\bar{k}_1),~\varrho _{2}=(k_1k_2+\bar{k}_1\bar{k}_2),\\ \varrho _{3}= & {} (k_1\bar{k}_2+k_2\bar{k}_1).\\ \text{ e }^{\mu _{4}^{(j)}}= & {} -\varrho _{12}\bar{\varrho }_{12}^2\bigg ((-1)^{j}k_1\beta _1^{(3-j)}\nu _1\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{11}+\bar{k}_1\alpha _1^{(j)}\varGamma _{21}\bigg )\\&\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2-\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )\bigg /\kappa \kappa _{11}\kappa _{12} ,\\ \text{ e }^{\mu _{5}^{(j)}}= & {} -\varrho _{12}\bar{\varrho }_{12}^2\bigg ((-1)^{j}k_2\beta _2^{(3-j)}\nu _1\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{12}+\bar{k}_1\alpha _1^{(j)}\varGamma _{22}\bigg )\\&\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2-\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )\bigg /\kappa \kappa _{21}\kappa _{22} \\ \text{ e }^{\varphi _{4}^{(j)}}= & {} -\varrho _{12}^2\bar{\varrho }_{12}\bigg (-k_2\beta _2^{(j)}\varGamma _{11}\\&+\,k_1\beta _1^{(j)}\varGamma _{12}+(-1)^{(3-j)}\bar{k}_1\alpha _1^{(3-j)}\nu _2\bigg )\\&\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2-\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )/\kappa \kappa _{11}\kappa _{21},\\ \text{ e }^{\varphi _{5}^{(j)}}= & {} -\varrho _{12}^2\bar{\varrho }_{12}\bigg (-k_2\beta _2^{(j)}\varGamma _{21}\\&+\,k_1\beta _1^{(j)}\varGamma _{22}+(-1)^{(3-j)}\bar{k}_2\alpha _2^{(3-j)}\nu _2\bigg )\\&\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2-\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )/\kappa \kappa _{12}\kappa _{22},\\ \text{ e }^{\delta _{31}}= & {} \varrho _{12}^2\bar{\varrho }_{12}^2\bigg (\varrho _{1}\varGamma _{11}\varGamma _{22}-\varrho _{2}\nu _1\nu _2\\&-\,\varrho _{3}\varGamma _{21}\varGamma _{12}\bigg )^2\bigg /\kappa _{11}^2\kappa _{12}^2\kappa _{21}^2\kappa _{22}^2,\\ \kappa= & {} \kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}. \end{aligned}$$
We arrive at the degenerate two-soliton solution by substituting the expression given in (31a)–(31c) in Eq. (4). The auxiliary functions are found to be
$$\begin{aligned}&s^{(1)}(-x,t)=s^{(2)}(-x,t)=\varGamma _{11}\text{ e }^{\xi _1+\bar{\xi }_1}+\varGamma _{21}\text{ e }^{\xi _1+\bar{\xi }_2}\\&\quad +\,\varGamma _{12}\text{ e }^{\bar{\xi }_1+\xi _2}+\varGamma _{22}\text{ e }^{\xi _2+\bar{\xi }_2}\\&\quad +\,\text{ e }^{\xi _1+2\bar{\xi }_1+\xi _2+\phi _1}+e^{2\xi _1+\bar{\xi }_1+\bar{\xi }_2+\phi _2}\\&\quad +\,\text{ e }^{\xi _1+\xi _2+2\bar{\xi }_2+\phi _3}+\text{ e }^{2\xi _2+\bar{\xi }_1+\bar{\xi }_2+\phi _4}\\&\quad +\,\text{ e }^{\xi _1+\bar{\xi }_1+\xi _2+\bar{\xi }_2+\phi _5}+\text{ e }^{2\xi _1+2\bar{\xi }_1+\xi _2+\bar{\xi }_2+\phi _{11}}\\&\quad +\,\text{ e }^{\xi _1+2\bar{\xi }_1+2\xi _2+\bar{\xi }_2+\phi _{12}}+\text{ e }^{2\xi _1+\bar{\xi }_1+\xi _2+2\bar{\xi }_2+\phi _{13}}\\&\quad +\,\text{ e }^{\xi _1+\bar{\xi }_1+2\xi _2+2\bar{\xi }_2+\phi _{14}} \end{aligned}$$
where the constants are obtained as
$$\begin{aligned} \text{ e }^{\phi _{1}}= & {} \frac{-\varrho _{12}^2\varGamma _{11}\varGamma _{12}}{\kappa _{11}\kappa _{21}},~\text{ e }^{\phi _{2}}=\frac{-\bar{\varrho }_{12}^2\varGamma _{11}\varGamma _{21}}{\kappa _{11}\kappa _{12}},\\ \text{ e }^{\phi _{3}}= & {} \frac{-\varrho _{12}^2\varGamma _{21}\varGamma _{22}}{\kappa _{12}\kappa _{22}},~\text{ e }^{\phi _{4}}=\frac{-\bar{\varrho }_{12}^2\varGamma _{12}\varGamma _{22}}{\kappa _{21}\kappa _{22}},\\ \text{ e }^{\phi _5}= & {} \frac{\varGamma _{11}\varGamma _{22}(\kappa _{12}\kappa _{21})^{1/2}\varLambda _1+\varGamma _{12}\varGamma _{21}(\kappa _{11}\kappa _{22})^{1/2}\varLambda _2}{\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}}, \end{aligned}$$
$$\begin{aligned} \varLambda _1= & {} (2\kappa _{11}(\kappa _{21}\kappa _{12})^{\frac{1}{2}}-\kappa _{11}\kappa _{12}^{\frac{1}{2}}(2\bar{k}_1+k_2-\bar{k}_2)\\&-\,\kappa _{11}\kappa _{21}^{\frac{1}{2}}(2k_1-k_2+\bar{k}_2)\\&+\,\kappa _{21}^{\frac{1}{2}}\kappa _{22}(-k_1+\bar{k}_1-2\bar{k}_2)\\&+\,(k_1-\bar{k}_1-2k_2)\kappa _{12}+2(\kappa _{12}\kappa _{21})^{\frac{1}{2}}\kappa _{22}),\\ \varLambda _2= & {} \left( \kappa _{11}^{\frac{1}{2}}(k_1-2k_2-\bar{k}_2)\kappa _{21}\right. \\&+\,\kappa _{11}^{\frac{1}{2}}\kappa _{12}(\bar{k}_1-k_2-2\bar{k}_2)\\&+\,2(\kappa _{11}\kappa _{22})^{\frac{1}{2}}\kappa _{21}-\kappa _{21}\kappa _{22}^{\frac{1}{2}}(k_1+2\bar{k}_1-\bar{k}_2)\\&\left. +\,2\kappa _{12}\kappa _{22}\kappa _{11}^{\frac{1}{2}}-(2k_1+\bar{k}_1-k_2)\kappa _{12}\kappa _{22}^{\frac{1}{2}}\right) ,\\ \text{ e }^{\phi _{11}}= & {} \frac{\varrho _{12}\bar{\varrho }_{12}\varGamma _{11}\psi }{\kappa _{11}^2\kappa _{21}\kappa _{12}},~\text{ e }^{\phi _{12}}=\frac{\varrho _{12}\bar{\varrho }_{12}\varGamma _{12}\psi }{\kappa _{11}\kappa _{21}^2\kappa _{22}},\\ \text{ e }^{\phi _{13}}= & {} \frac{\varrho _{12}\bar{\varrho }_{12}\varGamma _{21}\psi }{\kappa _{11}\kappa _{12}^2\kappa _{22}},~\text{ e }^{\phi _{14}}=\frac{\varrho _{12}\bar{\varrho }_{12}\varGamma _{22}\psi }{\kappa _{21}\kappa _{12}\kappa _{22}^2},\\ \psi= & {} \bigg (k_2\bar{k}_2\varGamma _{11}\varGamma _{22}+k_1(-\bar{k}_2\varGamma _{21}\varGamma _{12}\\&+\,\bar{k}_1\varGamma _{11}\varGamma _{22}-k_2\nu _1\nu _2)-\bar{k}_1(k_2\varGamma _{21}\varGamma _{12}+\bar{k}_2\nu _1\nu _2)\bigg ), \end{aligned}$$
D. The constants which appear in the degenerate three-soliton solution (24a)–(24c)
The constants which appear in factorized degenerate three-soliton solution (24a)–(24c) have the explicit forms,
$$\begin{aligned} \text{ e }^{\varDelta _1^{(j)}}= & {} \bar{\varrho }_{12}[(-1)^{3-j}k_1\beta _1^{(3-j)}\nu _1^{(1)}+\bar{k}_2\alpha _2^{(j)}\varGamma _{11}\\&-\,\bar{k}_1\alpha _1^{(j)}\varGamma _{21}]/\kappa _{11}\kappa _{12},\\ \text{ e }^{\varDelta _2^{(j)}}= & {} \bar{\varrho }_{13}[(-1)^{3-j}k_1\beta _1^{(3-j)}\nu _2^{(1)}+\bar{k}_3\alpha _3^{(j)}\varGamma _{11}\\&-\,\bar{k}_1\alpha _1^{(j)}\varGamma _{31}]/\kappa _{11}\kappa _{13},\\ \text{ e }^{\varDelta _3^{(j)}}= & {} \bar{\varrho }_{23}[(-1)^{3-j}k_1\beta _1^{(3-j)}\nu _3^{(1)}+\bar{k}_3\alpha _3^{(j)}\varGamma _{21}\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{31}]/\kappa _{12}\kappa _{13},\\ \text{ e }^{\varDelta _4^{(j)}}= & {} \bar{\varrho }_{12}[(-1)^{3-j}k_2\beta _2^{(3-j)}\nu _1^{(1)}+\bar{k}_2\alpha _2^{(j)}\varGamma _{12}\\&-\,\bar{k}_1\alpha _1^{(j)}\varGamma _{22}]/\kappa _{21}\kappa _{22},\\ \text{ e }^{\varDelta _5^{(j)}}= & {} \bar{\varrho }_{13}[(-1)^{3-j}k_2\beta _2^{(3-j)}\nu _2^{(1)}+\bar{k}_3\alpha _3^{(j)}\varGamma _{12}\\&-\,\bar{k}_1\alpha _1^{(j)}\varGamma _{32}]/\kappa _{21}\kappa _{23},\\ \text{ e }^{\varDelta _6^{(j)}}= & {} \bar{\varrho }_{23}[(-1)^{3-j}k_2\beta _2^{(3-j)}\nu _3^{(1)}+\bar{k}_3\alpha _3^{(j)}\varGamma _{22}\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{32}]/\kappa _{22}\kappa _{23},\\ \text{ e }^{\varDelta _7^{(j)}}= & {} \bar{\varrho }_{12}[(-1)^{3-j}k_3\beta _3^{(3-j)}\nu _1^{(1)}+\bar{k}_2\alpha _2^{(j)}\varGamma _{13}\\&-\,\bar{k}_1\alpha _1^{(j)}\varGamma _{23}]/\kappa _{31}\kappa _{32},\\ \end{aligned}$$
$$\begin{aligned} \text{ e }^{\varDelta _8^{(j)}}= & {} \bar{\varrho }_{13}[(-1)^{3-j}k_3\beta _3^{(3-j)}\nu _2^{(1)}+\bar{k}_3\alpha _3^{(j)}\varGamma _{13}\\&-\,\bar{k}_1\alpha _1^{(j)}\varGamma _{33}]/\kappa _{31}\kappa _{33},\\ \text{ e }^{\varDelta _9^{(j)}}= & {} \bar{\varrho }_{23}[(-1)^{3-j}k_3\beta _3^{(3-j)}\nu _3^{(1)}+\bar{k}_3\alpha _3^{(j)}\varGamma _{23}\\&-\,\bar{k}_2\alpha _2^{(j)}\varGamma _{33}]/\kappa _{32}\kappa _{33},\\ \text{ e }^{\gamma _1^{(j)}}= & {} \varrho _{12}[k_2\beta _2^{(j)}\varGamma _{11}-k_1\beta _1^{(j)}\varGamma _{12}\\&+\,(-1)^{(j)}\bar{k}_1\alpha _1^{(3-j)}\nu _1^{(2)}]/\kappa _{11}\kappa _{21},\\ \text{ e }^{\gamma _2^{(j)}}= & {} \varrho _{13}[k_3\beta _3^{(j)}\varGamma _{11}-k_1\beta _1^{(j)}\varGamma _{13}\\&+\,(-1)^{(j)}\bar{k}_1\alpha _1^{(3-j)}\nu _2^{(2)}]/\kappa _{11}\kappa _{31},\\ \text{ e }^{\gamma _3^{(j)}}= & {} \varrho _{23}[k_3\beta _3^{(j)}\varGamma _{12}-k_2\beta _2^{(j)}\varGamma _{13}\\&+\,(-1)^{(j)}\bar{k}_1\alpha _1^{(3-j)}\nu _3^{(2)}]/\kappa _{21}\kappa _{31},\\ \text{ e }^{\gamma _4^{(j)}}= & {} \varrho _{12}[k_2\beta _2^{(j)}\varGamma _{21}-k_1\beta _1^{(j)}\varGamma _{22}\\&+\,(-1)^{(j)}\bar{k}_2\alpha _2^{(3-j)}\nu _1^{(2)}]/\kappa _{12}\kappa _{22},\\ \text{ e }^{\gamma _5^{(j)}}= & {} \varrho _{13}[k_3\beta _3^{(j)}\varGamma _{21}-k_1\beta _1^{(j)}\varGamma _{23}\\&+\,(-1)^{(j)}\bar{k}_2\alpha _2^{(3-j)}\nu _2^{(2)}]/\kappa _{12}\kappa _{32},\\ \text{ e }^{\gamma _6^{(j)}}= & {} \varrho _{23}[k_3\beta _3^{(j)}\varGamma _{22}-k_2\beta _2^{(j)}\varGamma _{23}\\&+\,(-1)^{(j)}\bar{k}_2\alpha _2^{(3-j)}\nu _3^{(2)}]/\kappa _{22}\kappa _{32},\\ \text{ e }^{\gamma _7^{(j)}}= & {} \varrho _{12}[k_2\beta _2^{(j)}\varGamma _{31}-k_1\beta _1^{(j)}\varGamma _{32}\\&+\,(-1)^{(j)}\bar{k}_3\alpha _3^{(3-j)}\nu _1^{(2)}]/\kappa _{13}\kappa _{23}, \end{aligned}$$
$$\begin{aligned} \text{ e }^{\gamma _8^{(j)}}= & {} \varrho _{13}[k_3\beta _3^{(j)}\varGamma _{31}-k_1\beta _1^{(j)}\varGamma _{33}\\&+\,(-1)^{(j)}\bar{k}_3\alpha _3^{(3-j)}\nu _2^{(2)}]/\kappa _{13}\kappa _{33},\\ \text{ e }^{\gamma _9^{(j)}}= & {} \varrho _{23}[k_3\beta _3^{(j)}\varGamma _{32}-k_2\beta _2^{(j)}\varGamma _{33}\\&+\,(-1)^{(j)}\bar{k}_3\alpha _3^{(3-j)}\nu _3^{(2)}]/\kappa _{23}\kappa _{33},\\ \text{ e }^{\delta _{1}}= & {} -\frac{\varGamma _{11}}{\kappa _{11}},~\text{ e }^{\delta _{2}}=-\frac{\varGamma _{21}}{\kappa _{12}},~\text{ e }^{\delta _{3}}=-\frac{\varGamma _{31}}{\kappa _{13}},\\ \text{ e }^{\delta _{4}}= & {} -\frac{\varGamma _{12}}{\kappa _{21}},~\text{ e }^{\delta _{5}}=-\frac{\varGamma _{13}}{\kappa _{31}},\\ \text{ e }^{\delta _{6}}= & {} -\frac{\varGamma _{22}}{\kappa _{22}},~\text{ e }^{\delta _{7}}=-\frac{\varGamma _{32}}{\kappa _{23}}, \\ \text{ e }^{\delta _{8}}= & {} -\frac{\varGamma _{23}}{\kappa _{32}},~\text{ e }^{\delta _{9}}=-\frac{\varGamma _{33}}{\kappa _{33}},\\ \text{ e }^{\delta _{11}}= & {} \varrho _{12}\bar{\varrho }_{12}(\varrho _{1}\varGamma _{11}\varGamma _{22}\\&-\,\varrho _{2}\nu _1^{(1)}\nu _2^{(2)}-\varrho _{3}\varGamma _{21}\varGamma _{12})/\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22},\\ \text{ e }^{\delta _{12}}= & {} \varrho _{12}\bar{\varrho }_{13}(\varrho _{4}\varGamma _{11}\varGamma _{32}\\&-\,\varrho _{6}\nu _2^{(1)}\nu _1^{(2)}-\varrho _{5}\varGamma _{31}\varGamma _{12})/\kappa _{11}\kappa _{21}\kappa _{13}\kappa _{23},\\ \text{ e }^{\delta _{13}}= & {} \varrho _{12}\bar{\varrho }_{23}(\varrho _{9}\varGamma _{1}\varGamma _{32}\\&-\,\varrho _{7}\nu _3^{(1)}\nu _1^{(2)}-\varrho _{8}\varGamma _{31}\varGamma _{22})/\kappa _{12}\kappa _{22}\kappa _{13}\kappa _{23},\\ \text{ e }^{\delta _{14}}= & {} \varrho _{13}\bar{\varrho }_{12}(\varrho _{10}\varGamma _{11}\varGamma _{23}\\&-\,\varrho _{12}\nu _1^{(1)}\nu _2^{(2)}-\varrho _{11}\varGamma _{21}\varGamma _{13})/\kappa _{11}\kappa _{12}\kappa _{31}\kappa _{32},\\ \text{ e }^{\delta _{15}}= & {} \varrho _{23}\bar{\varrho }_{12}(\varrho _{13}\varGamma _{12}\varGamma _{23}\\&-\,\varrho _{15}\nu _1^{(1)}\nu _3^{(2)}-\varrho _{14}\varGamma _{22}\varGamma _{13})/\kappa _{21}\kappa _{22}\kappa _{31}\kappa _{32},\\ \text{ e }^{\delta _{16}}= & {} \varrho _{13}\bar{\varrho }_{13}(\varrho _{16}\varGamma _{11}\varGamma _{33}\\&-\,\varrho _{18}\nu _2^{(1)}\nu _2^{(2)}-\varrho _{17}\varGamma _{31}\varGamma _{13})/\kappa _{11}\kappa _{31}\kappa _{13}\kappa _{33},\\ \text{ e }^{\delta _{17}}= & {} \varrho _{23}\bar{\varrho }_{13}(\varrho _{19}\varGamma _{12}\varGamma _{33}\\&-\,\varrho _{21}\nu _2^{(1)}\nu _3^{(2)}-\varrho _{20}\varGamma _{32}\varGamma _{13})/\kappa _{21}\kappa _{31}\kappa _{23}\kappa _{33},\\ \text{ e }^{\delta _{18}}= & {} \varrho _{13}\bar{\varrho }_{23}(\varrho _{22}\varGamma _{21}\varGamma _{33}\\&-\,\varrho _{24}\nu _3^{(1)}\nu _2^{(2)}-\varrho _{23}\varGamma _{31}\varGamma _{23})/\kappa _{12}\kappa _{32}\kappa _{13}\kappa _{33},\\ \text{ e }^{\delta _{19}}= & {} \varrho _{23}\bar{\varrho }_{23}(\varrho _{25}\varGamma _{22}\varGamma _{33}\\&-\,\varrho _{27}\nu _3^{(1)}\nu _3^{(2)}-\varrho _{26}\varGamma _{32}\varGamma _{23})/\kappa _{22}\kappa _{32}\kappa _{23}\kappa _{33},\\ \end{aligned}$$
$$\begin{aligned} \text{ e }^{\chi _1^{(j)}}= & {} \frac{\varrho _{12}\bar{\varrho }_{12}\bar{\varrho }_{13}\bar{\varrho }_{23}\varLambda _1^{(j)}}{\kappa _{11}\kappa _{12}\kappa _{21}\kappa _{22}\kappa _{13}\kappa _{23}},~\text{ e }^{\chi _2^{(j)}}=\frac{\varrho _{13}\bar{\varrho }_{12}\bar{\varrho }_{13}\bar{\varrho }_{23}\varLambda _2^{(j)}}{\kappa _{11}\kappa _{12}\kappa _{31}\kappa _{32}\kappa _{13}\kappa _{33}},\\ \text{ e }^{\chi _3^{(j)}}= & {} \frac{\varrho _{23}\bar{\varrho }_{12}\bar{\varrho }_{13}\bar{\varrho }_{23}\varLambda _3^{(j)}}{\kappa _{21}\kappa _{22}\kappa _{31}\kappa _{32}\kappa _{23}\kappa _{33}},~\text{ e }^{\varphi _1^{(j)}}=\frac{\bar{\varrho }_{12}\varrho _{12}\varrho _{13}\varrho _{23}\varLambda _4^{(j)}}{\kappa _{11}\kappa _{21}\kappa _{12}\kappa _{22}\kappa _{31}\kappa _{32}},\\ \text{ e }^{\varphi _2^{(j)}}= & {} \frac{\bar{\varrho }_{13}\varrho _{12}\varrho _{13}\varrho _{23}\varLambda _5^{(j)}}{\kappa _{11}\kappa _{21}\kappa _{31}\kappa _{13}\kappa _{23}\kappa _{33}},~\text{ e }^{\varphi _3^{(j)}}=\frac{\bar{\varrho }_{23}\varrho _{12}\varrho _{13}\varrho _{23}\varLambda _6^{(j)}}{\kappa _{12}\kappa _{22}\kappa _{32}\kappa _{13}\kappa _{23}\kappa _{33}},\\ \varLambda _1^{(j)}= & {} (-1)^{(3-j)}k_2\bar{k}_2\bar{k}_3\varGamma _{11}\big [(-1)^{j}k_2\beta _2^{(3-j)}\nu _3^{(1)}\\&-\,\bar{k}_3\alpha _3^{(j)}\varGamma _{22}+\bar{k}_2\alpha _2^{(j)}\varGamma _{32}\big ]\\&+\,\bar{k}_1\big [k_2^2\beta _2^{(3-j)}\big (\bar{k}_3\nu _2^{(1)}\varGamma _{21}-\bar{k}_2\nu _1^{(1)}\varGamma _{11}\big )\\&+\,(-1)^jk_2\varGamma _{12}\big (-\bar{k}_3^2\alpha _3^{(j)}\varGamma _{21}+\bar{k}_2^2\alpha _2^{(j)}\varGamma _{31}\big )\\&+\,(-1)^j\bar{k}_2\bar{k}_3\nu _1^{(2)}\big (-\bar{k}_3\nu _1^{(1)}\alpha _3^{(j)}+\bar{k}_2\alpha _2^{(j)}\nu _2^{(1)}\big )\big ]\\&+\,k_1^2\beta _1^{(3-j)}\big [\bar{k}_2\bar{k}_3\nu _3^{(1)}\varGamma _{12}+\bar{k}_1\big (-k_2\nu _3^{(1)} \varGamma _{12}\\&-\,\bar{k}_3\nu _2^{(1)}\varGamma _{22}+\bar{k}_2\nu _1^{(1)}\varGamma _{32} \big )+k_2\big (\bar{k}_2\nu _2^{(1)}\varGamma _{22}\\&-\,\bar{k}_3\nu _1^{(1)}\varGamma _{32}\big )\big ]+\bar{k}_1^2\alpha _1^{(j)}\big [(-1)^{(3-j)}\bar{k}_2\bar{k}_3\nu _3^{(1)}\\&\nu _1^{(2)}+(-1)^{(3-j)}k_2\big (\bar{k}_2\varGamma _{31}\varGamma _{22}-\bar{k}_3\varGamma _{21}\varGamma _{32}\big )\big ]\\&+\,k_1\big [\bar{k}_2\varGamma _{21}\big (-k_2^2\nu _2^{(1)}\beta _2^{(3-j)}+(-1)^{(3-j)}\bar{k}_3^2\alpha _3^{(j)}\varGamma _{12}\big )\\&+\,\bar{k}_1\varGamma _{11}\big (k_2^2\nu _3^{(1)}\beta _2^{(3-j)}+(-1)^{(j)}\bar{k}_3^2\alpha _3^{(j)}\varGamma _{22}\\&+\,(-1)^{(3-j)}\bar{k}_2^2\alpha _2^{(j)}\varGamma _{32}\big )+(-1)^{(j)}\bar{k}_2^2\alpha _2^{(j)}\big (\bar{k}_3\varGamma _{31}\varGamma _{12}\\&+\,k_2\nu _2^{(1)}\nu _1^{(2)}\big )+(-1)^{(3-j)}\bar{k}_1^2\alpha _1^{(j)}\big (\bar{k}_3\varGamma _{31}\varGamma _{22}\\&+\,\bar{k}_2\varGamma _{21}\varGamma _{32}+k_2\nu _3^{(1)}\nu _1^{(2)}\big )\\&+\,k_2\bar{k}_3\nu _1^{(1)}\big (k_2\varGamma _{31}\beta _2^{3-(j)}+(-1)^{(3-j)}\bar{k}_3\alpha _3^{(j)}\nu _1^{(2)}\big )\big ], \end{aligned}$$
$$\begin{aligned} \varLambda _2^{(j)}= & {} -\,\bar{k}_2k_3\bar{k}_3\varGamma _{11}\big [(-1)^{(j)}k_3\nu _3^{(1)}\beta _3^{(3-j)}\\&-\,\bar{k}_3\alpha _3^{(j)}\varGamma _{23}+\bar{k}_2\alpha _2^{(j)}\varGamma _{33}\big ]\\&+\,k_1^2\beta _1^{(3-j)}\big [(-1)^{(3-j)}k_3\bar{k}_3\nu _1^{(1)}\varGamma _{33}\\&+\,(-1)^{(j)}\bar{k}_2\big (\bar{k}_3\nu _3^{(1)}\varGamma _{13}+k_3\\&\nu _2^{(1)}\varGamma _{23}\big )+(-1)^{(3-j)}\bar{k}_1\big (k_3\nu _3^{(1)}\varGamma _{13}\\&+\,\bar{k}_3\nu _2^{(1)}\varGamma _{23}+(-1)^{(j)}\bar{k}_2\nu _1^{(1)}\\&\varGamma _{33}\big )\big ]+\bar{k}_1\big [(-1)^{(j)}k_3\bar{k}_3\varGamma _{21}\big (k_3\nu _2^{(1)}\beta _3^{(3-j)}\\&+\,(-1)^{(3-j)}\bar{k}_3\alpha _3^{(j)}\varGamma _{13}\big )+\bar{k}_2^2\alpha _2^{(j)}\big (k_3\varGamma _{13}\varGamma _{31}\\&+\,\bar{k}_3\nu _2^{(1)}\nu _2^{(2)}\big )+(-1)^{(3-j)}\big (k_3^2\varGamma _{31}\beta _3^{(3-j)}\\&+\,(-1)^{(3-j)}\alpha _3^{(j)}\nu _2^{(2)}\big )\big ]\nonumber \\&+\,\bar{k}_1^2\alpha _1^{(j)}\big [k_3\bar{k}_3\varGamma _{21}\varGamma _{33}-\bar{k}_2\big (k_3\varGamma _{31}\varGamma _{23}+\bar{k}_3\nu _3^{(1)}\nu _2^{(2)}\big )\big ]\\&+\,k_1\big [-\bar{k}_2\varGamma _{21}\big ((-1)^{(j)}k_3^2\nu _2^{(1)}\beta _3^{(3-j)}+\bar{k}_3^2\alpha _3^{(j)}\varGamma _{13}\big )\\&+\,\bar{k}_1\varGamma _{11}\big ((-1)^{(j)}k_3^2\nu _3^{(1)}\beta _3^{(3-j)}+\bar{k}_3^2\alpha _3^{(j)}\varGamma _{23}\\&-\,\bar{k}_2^2\alpha _2^{(j)}\varGamma _{33}\big )+(-1)^{(j)}k_3\\&\bar{k}_3\nu _1^{(1)}\big (k_3\varGamma _{31}\beta _3^{(3-j)}+(-1)^{(3-j)}\bar{k}_3\alpha _3^{(j)}\nu _2^{(2)}\big )\\&+\,\bar{k}_2\alpha _2^{(j)} \big (\bar{k}_3\varGamma _{31}\varGamma _{13}+k_3\nu _2^{(1)}\nu _1^{(2)}\big )\\&+\,\bar{k}_1^2\alpha _1^{(j)}\big (-\bar{k}_3\varGamma _{31}\varGamma _{23}+\bar{k}_2\varGamma _{21}\varGamma _{33}\\&-\,k_3\nu _3^{(1)}\nu _2^{(2)}\big )\big ],\\ \varLambda _3^{(j)}= & {} -\,\bar{k}_2k_3\bar{k}_3\varGamma _{12}\big [(-1)^{(j)}k_3\nu _3^{(1)}\beta _3^{(3-j)}\\&-\,\bar{k}_3\alpha _3^{(j)}\varGamma _{23}+\bar{k}_2\alpha _2^{(j)}\varGamma _{33}\big ]\\&+\,k_2^2\beta _2^{(3-j)}\big [(-1)^{(3-j)}k_3\bar{k}_3\nu _1^{(1)}\varGamma _{33}\\&+\,\bar{k}_2\big ((-1)^{(j)}\bar{k}_3\nu _3^{(1)}\varGamma _{13}+(-1)^{(j)}k_3\nu _2^{(1)}\varGamma _{23}\big )\big ]\\&+\,\bar{k}_1\big [(-1)^{(j)}k_3\bar{k}_3\varGamma _{22}\big (k_3\nu _2^{(1)}\beta _3^{(3-j)}+(-1)^{(3-j)}\\&\bar{k}_3\alpha _3^{(j)}\varGamma _{13}\big )+k_2\varGamma _{12}\big ((-1)^{(j)}k_3^2\nu _3^{(1)}\beta _3^{(3-j)}\\&+\,\bar{k}_3^2\alpha _3^{(j)}\varGamma _{23}-\bar{k}_2^2\alpha _2^{(j)}\varGamma _{33}\big )\\ \end{aligned}$$
$$\begin{aligned}&+\,k_2^2\beta _2^{(3-j)}\big ((-1)^{(3-j)}k_3\nu _3^{(1)}\varGamma _{13}\\&+\,(-1)^{(3-j)}\bar{k}_3\nu _2^{(1)}\varGamma _{23}+(-1)^{(j)}\\&\bar{k}_2\nu _1^{(1)}\varGamma _{33}\big )+(-1)^{(3-j)}\bar{k}_2\nu _1^{(1)}\big (k_3^2\varGamma _{32}\beta _3^{(3-j)}\\&+\,(-1)^{(j)}\bar{k}_3^2\alpha _3^{(j)}\nu _3^{(2)}\big )\\&+\,\bar{k}_2^2\alpha _2^{(j)}\big (k_3\varGamma _{32}\varGamma _{13}+\bar{k}_3\nu _2^{(1)}\nu _3^{(2)}\big )\big ]\\&+\,\bar{k}_1^2\alpha _1^{(j)}\big [k_3\bar{k}_3\varGamma _{22}\varGamma _{33}+k_2\big (-\bar{k}_3\\&\varGamma _{32}\varGamma _{23}+\bar{k}_2\varGamma _{22}\varGamma _{33}-k_3\nu _3^{(1)}\nu _3^{(2)}\big )\\&-\,\bar{k}_2\big (k_3\varGamma _{32}\varGamma _{23}+\bar{k}_3\nu _3^{(1)}\nu _3^{(2)}\big )\big ]\\&+\,k_2\big [-\bar{k}_2\varGamma _{22}\big ((-1)^{(j)}k_3^2\nu _2^{(1)}\beta _3^{(3-j)}\\&+\,\bar{k}_3^2\alpha _3^{(j)}\varGamma _{13}\big )+(-1)^{(j)}k_3\bar{k}_3\nu _1^{(1)}\\&\big (k_3\varGamma _{32}\beta _3^{(3-j)}+\bar{k}_3\alpha _3^{(j)}\nu _3^{(2)}\big )\\&+\,\bar{k}_2^2\alpha _2^{(j)}\big (\bar{k}_3\varGamma _{32}\varGamma _{13}+k_3\nu _2^{(1)}\nu _3^{(2)}\big )\big ],\\ \varLambda _4^{(j)}= & {} -\,k_2\bar{k}_2k_3\varGamma _{11}\big [-k_3\varGamma _{22}\beta _3^{(j)}\\&+\,k_2\beta _2^{(j)}\varGamma _{23}+(-1)^{(3-j)}\alpha _2^{(3-j)}\bar{k}_2\nu _3^{(2)}\big ]\\&+\,\bar{k}_1\big [(-1)^{(3-j)}\bar{k}_2k_3\nu _1^{(2)}\big ((-1)^{(j)}k_3\nu _1^{(1)}\beta _3^{(j)}\\&+\,\bar{k}_2\alpha _2^{(j)}\varGamma _{13}\big )+k_2^2\\&\beta _2^{(j)}\big (k_3\varGamma _{21}\varGamma _{13}+\bar{k}_2\nu _1^{(1)}\nu _1^{(2)}\big )\\&-\,k_2\varGamma _{12}\big (k_3^2\varGamma _{21}\beta _3^{(j)}+(-1)^{(3-j)}\\&\bar{k}_2^2\alpha _2^{(3-j)}\nu _2^{(2)}\big )\big ]+k_1^2\beta _1^{(j)}\big [\bar{k}_2k_3\varGamma _{12}\varGamma _{23}\\&+\,\bar{k}_1\big (-k_3\varGamma _{22}\varGamma _{13}+k_2\varGamma _{12}\varGamma _{23}\\&-\,\bar{k}_2\nu _1^{(1)}\nu _3^{(2)}\big )-k_2\big (\bar{k}_2\varGamma _{22}\varGamma _{13}\\&+\,k_3\nu _1^{(1)}\nu _3^{(2)}\big )\big ]+\bar{k}_1^2\alpha _1^{(3-j)}\big [(-1)^{(j)}\bar{k}_2k_3\\&\nu _1^{(2}\varGamma _{23}+(-1)^{(3-j)}k_2\big (\bar{k}_2\varGamma _{22}\nu _2^{(2)}\\&+\,k_3\varGamma _{21}\nu _3^{(2)}\big )\big ]+k_1\big [(-1)^{(j)}k_2\nu _1^{(2)}\\&\big ((-1)^{(3-j)}k_3^2\nu _1^{(1)}\beta _3^{(j)}+\bar{k}_2^2\alpha _2^{(3-j)}\varGamma _{13}\big )\\&-\,\bar{k}_2k_3\varGamma _{12}\big (k_3\varGamma _{21}\beta _3^{(j)}+(-1)^{(j)}\\&\bar{k}_2\alpha _2^{(j)}\nu _2^{(2)}\big )+k_2^2\beta _2^{(j)}\big (\bar{k}_2\varGamma _{21}\varGamma _{13}\\&+\,k_3\nu _1^{(1)}\nu _2^{(2)}\big )+\bar{k}_1^2\alpha _1^{(3-j)}\big ((-1)^{(3-j)}\\&k_2\nu _1^{(2)}\varGamma _{23}+(-1)^{(j)}k_3\varGamma _{22}\nu _3^{(2)}\\&+\,(-1)^{(j)}\bar{k}_2\varGamma _{21}\nu _3^{(2)}\big )+\bar{k}_1\varGamma _{11}\big (k_3^2\varGamma _{22}\\&\beta _3^{(j)}-k_2^2\beta _2^{(j)}\varGamma _{23}+(-1)^{(3-j)}\bar{k}_2^2\alpha _2^{(3-j)}\nu _3^{(2)}\big )\big ], \end{aligned}$$
$$\begin{aligned} \varLambda _5^{(j)}= & {} -\,k_2\bar{k}_3k_3\varGamma _{11}\big [-k_3\varGamma _{32}\beta _3^{(j)}+k_2^{(j)}\beta _2^{(j)}\varGamma _{33}\\&-\bar{k}_3\alpha _3^{(3-j)}\nu _3^{(2)}\big ]+\bar{k}_1\big [-k_3\bar{k}_3\\&\nu _1^{(2)}\big (k_3\beta _3^{(j)}\nu _2^{(1)}+(-1)^{(j)}\bar{k}_3\alpha _3^{(3-j)}\varGamma _{13}\big )\\&+\,k_2^2\beta _2^{(j)}\big (k_3\varGamma _{31}\varGamma _{13}+\bar{k}_3\nu _2^{(1)}\nu _2^{(2)}\big )\\&-\,k_2\varGamma _{12}\big (k_3^2\varGamma _{31}\beta _3^{(j)}+(-1)^{(3-j)}\bar{k}_3^2\alpha _3^{(3-j)}\nu _2^{(2)}\big )\big ]\\&+\,k_1^2\beta _1^{(j)}\big [k_3\bar{k}_3\varGamma _{12}\varGamma _{33}\\&-\,k_2\big (\bar{k}_3\varGamma _{32}\varGamma _{13}+k_3\nu _2^{(1)}\nu _3^{(2)}\big )+\bar{k}\big (-k_3\varGamma _{32}\varGamma _{13}\\&+\,k_2\varGamma _{12}\varGamma _{33}-\bar{k}_3\nu _2^{(1)}\nu _3^{(2)}\big )\big ]\\&+\,\bar{k}_1^2\alpha _1^{(3-j)}\big [(-1)^{(j)}k_3\bar{k}_3\nu _1^{(2)}\varGamma _{33}\\&+\,k_2\big ((-1)^{(3-j)}\bar{k}_3\varGamma _{32}\nu _2^{(2)}+(-1)^{(j)}k_3\varGamma _{31}\\&\nu _3^{(2)}\big )\big ]+k_1\big [(-1)^{(j)}k_2\nu _1^{(2)}\big ((-1)^{(3-j)}k_3^2\nu _2^{(1)}\beta _3^{(j)}\\&+\,\bar{k}_3^2\alpha _3^{(3-j)}\varGamma _{13}\big )-k_3\bar{k}_3\varGamma _{12}\\&\big (k_3\varGamma _{31}\beta _3^{(j)}+(-1)^{(j)}\bar{k}_3\alpha _3^{(3-j)}\nu _2^{(2)}\big )\\&+\,k_2^2\beta _2^{(j)}\big (\bar{k}_3\varGamma _{31}\varGamma _{13}+k_3\nu _2^{(1)}\nu _2^{(2)}\big )\\&+\,\bar{k}_1^2\alpha _1^{(3-j)}\big ((-1)^{(3-j)}k_2\nu _1^{(2)}\varGamma _{33}\\&+\,(-1)^{(j)}k_3\varGamma _{32}\nu _2^{(2)}+(-1)^{(j)}\bar{k}_3\varGamma _{31}\nu _3^{(2)}\big )\\&+\,\bar{k}_1\varGamma _{11}\big (k_3^2\varGamma _{32}\beta _3^{(j)}-k_2^2\beta _2^{(j)}\varGamma _{33}\\&+\,(-1)^{(3-j)}\bar{k}_3^2\alpha _3^{(3-j)}\nu _3^{(2)}\big )\big ],\\ \varLambda _6^{(j)}= & {} (-1)^{(j)}\bar{k}_2\bar{k}_3k_3\nu _1^{(2)}\big [(-1)^{(3-j)}k_3\nu _3^{(1)}\beta _3^{(j)}\\&-\,\bar{k}_3\alpha _3^{(3-j)}\varGamma _{23}+\bar{k}_2\alpha _2^{(3-j)}\varGamma _{33}\big ]\\&+\,k_2^2\beta _2^{(j)}\big [-k_3\bar{k}_3\varGamma _{21}\varGamma _{33}+\bar{k}_2\big (k_3\varGamma _{31}\varGamma _{23}\\&+\,\bar{k}_3\nu _3^{(1)}\nu _2^{(2)}\big )\big ]+k_1^2\beta _1^{(j)}\big [k_3\bar{k}_3\varGamma _{22}\\&\varGamma _{33}+k_2\big (-\bar{k}_3\varGamma _{32}\varGamma _{23}+\bar{k}_2\varGamma _{22}\varGamma _{33}-\,k_3\nu _3^{(1)}\nu _3^{(2)}\big )\\&-\,\bar{k}_2\big (k_3\varGamma _{32}\varGamma _{23}+\bar{k}_3\nu _3^{(1)}\\&\nu _3^{(2)}\big )\big ]+k_1\big [-k_2\nu _1^{(2)}\big (k_3^2\nu _3^{(1)}\beta _3^{(j)}\\&+\,(-1)^{(3-j)}\bar{k}_3^2\alpha _3^{(3-j)}\varGamma _{23}+(-1)^{(j)}\\ \end{aligned}$$
$$\begin{aligned}&\bar{k}_2^2\alpha _2^{(3-j)}\varGamma _{33}\big )-k_3\bar{k}_3\varGamma _{22}\big (k_3\varGamma _{31}\beta _3^{(3-j)}\\&+\,(-1)^{(j)}\bar{k}_3\alpha _3^{(3-j)}\nu _2^{(2)}\big )+k_2^2\beta _2^{(j)}\\&\big (\bar{k}_3\varGamma _{31}\varGamma _{23}-\bar{k}_2\varGamma _{21}\varGamma _{33}+k_3\nu _3^{(1)}\nu _2^{(2)}\big )\\&+\,\bar{k}_2^2\alpha _2^{(3-j)}\big ((-1)^{(j)}k_3\varGamma _{32}\nu _2^{(2)}\\&+\,(-1)^{(j)}\bar{k}_3\varGamma _{31}\nu _3^{(2)}\big )+\bar{k}_2\varGamma _{21}\big (k_3^2\varGamma _{32}\beta _3^{(j)}\\&+\,(-1)^{(3-j)}\bar{k}_3^2\alpha _3^{(3-j)}\nu _3^{(2)}\big )\big ]\\&+\,k_2\big [-\bar{k}_2\varGamma _{22}\big (k_3^2\varGamma _{31}\beta _3^{(j)}\\&+\,(-1)^{(3-j)}\bar{k}_3^2\alpha _3^{(3-j)}\nu _2^{(2)}\big )+k_3\bar{k}_3\varGamma _{21}\big (k_3\varGamma _{32}\\&\beta _3^{(j)}+(-1)^{(j)}\bar{k}_3\alpha _3^{(3-j)}\nu _3^{(2)}\big )\\&+\,\bar{k}_2^2\alpha _2^{(3-j)}\big ((-1)^{(3-j)}\bar{k}_3\varGamma _{32}\nu _2^{(2)}\\&+\,(-1)^{(3-j)}k_3\varGamma _{31}\nu _3^{(2)}\big )\big ],\\ \text{ e }^{\delta _{20}}= & {} \frac{-\varLambda _{71}}{(k_1+\bar{k}_1+k_2+\bar{k}_2+k_3+\bar{k}_3)^2},\\ \varLambda _{71}= & {} (-k_1-\bar{k}_1+k_2+\bar{k}_2+k_3+\bar{k}_3)^2\text{ e }^{\delta _{19}+\delta _1}\\&+\,(-k_1+\bar{k}_1+k_2-\bar{k}_2+k_3+\bar{k}_3)^2\\&\text{ e }^{\delta _{17}+\delta _2}+(-k_1+\bar{k}_1+k_2+\bar{k}_2+k_3\\&-\,\bar{k}_3)^2\text{ e }^{\delta _3+\delta _{15}}+\text{ e }^{\delta _4+\delta _{18}}\\&(k_1-\bar{k}_1-k_2+\bar{k}_2+k_3+\bar{k}_3)^2+\text{ e }^{\delta _5+\delta _{13}}\\&(k_1-\bar{k}_1+k_2+\bar{k}_2-k_3+\bar{k}_3)^2\\&+\,(k_1+\bar{k}_1-k_2-\bar{k}_2+k_3+\bar{k}_3)^2\text{ e }^{\delta _6+\delta _{16}}\\&+\,(k_1+\bar{k}_1-k_2+\bar{k}_2+k_3-\bar{k}_3)^2\\&\text{ e }^{\delta _7+\delta _{14}}+(k_1+\bar{k}_1+k_2-\bar{k}_2-k_3\\&+\,\bar{k}_3)^2\text{ e }^{\delta _8+\delta _{12}}+\text{ e }^{\delta _9+\delta _{11}}\\&(k_1+\bar{k}_1+k_2+\bar{k}_2-k_3-\bar{k}_3)^2+\text{ e }^{\gamma _9^{(1)}+\varDelta _1^{(1)}}\\&+\,\text{ e }^{\gamma _9^{(2)}+\varDelta _1^{(2)}}+\text{ e }^{\gamma _6^{(1)}+\varDelta _2^{(1)}}\\&+\,\text{ e }^{\gamma _6^{(2)}+\varDelta _2^{(2)}}+\text{ e }^{\gamma _3^{(1)}+\varDelta _3^{(1)}}+\text{ e }^{\gamma _3^{(2)}+\varDelta _3^{(2)}}\\&+\,\text{ e }^{\gamma _8^{(1)}+\varDelta _4^{(1)}}+\text{ e }^{\gamma _8^{(2)}+\varDelta _4^{(2)}}\\&+\,\text{ e }^{\gamma _5^{(1)}+\varDelta _5^{(1)}}+\text{ e }^{\gamma _5^{(2)}+\varDelta _5^{(2)}}++\text{ e }^{\gamma _2^{(1)}+\varDelta _6^{(1)}}\\&+\,\text{ e }^{\gamma _2^{(2)}+\varDelta _6^{(2)}}++\text{ e }^{\gamma _7^{(1)}+\varDelta _7^{(1)}}\\&+\,\text{ e }^{\gamma _7^{(2)}+\varDelta _7^{(2)}}+\text{ e }^{\gamma _4^{(1)}+\varDelta _8^{(1)}}+\text{ e }^{\gamma _4^{(2)}+\varDelta _8^{(2)}}\\&+\,e^{\gamma _1^{(1)}+\varDelta _9^{(1)}}+\text{ e }^{\gamma _1^{(2)}+\varDelta _9^{(2)}}\\&+\,\sum _{j=1}^{2}\alpha _3^{(j)}\text{ e }^{\varphi _1^{(j)}}+\sum _{j=1}^{2}\alpha _2^{(j)}\text{ e }^{\varphi _2^{(j)}}\\&+\,\sum _{j=1}^{2}\alpha _1^{(j)}\text{ e }^{\varphi _3^{(j)}}+\sum _{j=1}^{2}\beta _3^{(j)}\text{ e }^{\chi _1^{(j)}}\\&+\,\sum _{j=1}^{2}\beta _2^{(j)}\text{ e }^{\chi _2^{(j)}}+\sum _{j=1}^{2}\beta _1^{(j)}\text{ e }^{\chi _3^{(j)}},\\ \end{aligned}$$
$$\begin{aligned} \varGamma _{nm}= & {} (\alpha _n^{(1)}\beta _{m}^{(1)}\!+\!\alpha _n^{(2)}\beta _{m}^{(2)}),\kappa _{nm}\!=\!(k_n\!+\! \bar{k}_m)^2,~n\!=\!m\!=\!1,2,3,\\ \nu _1^{(1)}= & {} \alpha _1^{(2)}\alpha _2^{(1)}-\alpha _1^{(1)}\alpha _2^{(2)},~\nu _2^{(1)}=\alpha _1^{(2)}\alpha _3^{(1)}-\alpha _1^{(1)}\alpha _3^{(2)},\\ \nu _3^{(1)}= & {} \alpha _2^{(2)}\alpha _3^{(1)}-\alpha _2^{(1)}\alpha _3^{(2)},~\nu _1^{(2)}=\beta _1^{(1)}\beta _2^{(2)}-\beta _1^{(2)}\beta _2^{(1)},\\ \nu _2^{(2)}= & {} \beta _1^{(1)}\beta _3^{(2)}-\beta _1^{(2)}\beta _3^{(1)},~\nu _3^{(2)}=\beta _2^{(1)}\beta _3^{(2)}-\beta _2^{(2)}\beta _2^{(1)},\\ \varrho _1= & {} k_1\bar{k}_1+k_2\bar{k}_2,~\varrho _2=k_1k_2+\bar{k_1}\bar{k}_2,\\ \varrho _3= & {} k_1\bar{k}_2+k_2\bar{k}_1,~\varrho _4=k_2\bar{k}_3+k_1\bar{k}_1,\\ \varrho _5= & {} k_1\bar{k}_3+k_2\bar{k}_1,~\varrho _6=k_1k_2+\bar{k}_1\bar{k}_3,\\ \varrho _7= & {} k_1k_2+\bar{k}_2\bar{k}_3,~\varrho _8=k_2\bar{k}_2+k_1\bar{k}_3,\\ \varrho _9= & {} k_2\bar{k}_3+k_1\bar{k}_2,~\varrho _{10}=k_3\bar{k}_2+k_1\bar{k}_1,\\ \varrho _{11}= & {} k_3\bar{k}_1+k_1\bar{k}_2,~\varrho _{12}=k_3k_1+\bar{k}_2\bar{k}_1,\\ \varrho _{13}= & {} k_3\bar{k}_2+k_2\bar{k}_1,~\varrho _{14}=k_3\bar{k}_1+k_2\bar{k}_2,\\ \varrho _{15}= & {} \bar{k}_1\bar{k}_2+k_2k_3,~\varrho _{16}=k_3\bar{k}_3+k_1\bar{k}_1,\\ \varrho _{17}= & {} k_1\bar{k}_3+k_3\bar{k}_1,~\varrho _{18}=k_3k_1+\bar{k}_1\bar{k}_1,\\ \varrho _{19}= & {} k_3\bar{k}_3+k_2\bar{k}_1,~\varrho _{20}=k_2\bar{k}_3+k_3\bar{k}_1,\\ \varrho _{21}= & {} k_2k_3+\bar{k}_3\bar{k}_1,~\varrho _{22}=k_3\bar{k}_3+k_1\bar{k}_2,\\ \varrho _{23}= & {} k_1\bar{k}_3+k_3\bar{k}_2,~\varrho _{24}=k_3k_1+\bar{k}_2\bar{k}_3,\\ \varrho _{25}= & {} k_3\bar{k}_3+k_2\bar{k}_2,~\varrho _{26}=k_2\bar{k}_3+k_3\bar{k}_2,\\ \varrho _{27}= & {} k_2k_3+\bar{k}_2\bar{k}_3,\\ \varrho _{12}= & {} (k_1-k_2),~\varrho _{13}=(k_1-k_3),\\ \varrho _{23}= & {} (k_2-k_3),~\bar{\varrho }_{12}=(\bar{k}_1-\bar{k}_2),\\ \bar{\varrho }_{13}= & {} (\bar{k}_1-\bar{k}_3),~\bar{\varrho }_{23}=(\bar{k}_2-\bar{k}_3). \end{aligned}$$