A functionf from the posetP to the posetQ is a strict morphism if for allx, y ∈ P withx<y we havef(x)<f(y). If there is such a strict morphism fromP toQ we writeP → Q, otherwise we writeP \(\not \to \) Q. We say a posetM is multiplicative if for any posetsP, Q withP \(\not \to \) M andQ \(\not \to \) M we haveP ×Q \(\not \to \) M. (Here (p 1,q 1)<(p 2,q 2) if and only ifp 1<p 2 andq 1<q 2.) This paper proves that well-founded trees with height ≤ω are multiplicative posets.
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This research was supported in part by NSERC Grant #69-1325.
Communicated by E. C. Milner
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Sauer, N.W., Zhu, X. Multiplicative posets. Order 8, 349–358 (1991). https://doi.org/10.1007/BF00571185
Mathematics Subject Classification (1991)
- strict morphisms
- Hedetniemi's conjecture