Erratum to: Z. Zhang, Variational, Topological, and Partial Order Methods with Their Applications, Developments in Mathematics 29, pp. 1–33, DOI 10.1007/978-3-642-30709-6_1 , © Springer-Verlag Berlin Heidelberg 2013

The presentation of Definition 1.6.2 was incorrect. The correct version is given below.

FormalPara Definition 1.6.2

Assume \(L\in\mathcal{F}(X,Y)\), let

$$ \operatorname{ind}(L)\triangleq \operatorname{dim\ Ker} L-\operatorname{dim\ Coker} L, $$

it is called the index of L.