Let $G, H$ be two finite, simple, undirected graphs. We call them "reduce-by-1"-isomorphic, or $r\_1$-isomorphic for short, if there is a bijection $\psi: V(G) \to V(H)$ such that for all $v \in V(G)$ we have that $G \setminus \{v\}$ is isomorphic to $H \setminus \{\psi(v)\}$.


(Ulam's reconstruction conjecture, or some version of it, states that $r\_1$-isomorphic implies isomorphic.)


Can we prove that if $G, H$ are $r\_1$-isomorphic then they have the same chromatic number?


**EDIT**: Will ask about Hadwiger number in different post, it's better to ask one question per post.



"Reduce-by-1"-isomorphic graphs
The chromatic polynomial, and therefore the chromatic number, was proved reconstructible by Tutte in his famous paper "All the king's horses". I don't know about the Hadwiger number.


