16 May
2020
16 May
'20
12:51 p.m.
Dan Asimov <dasimov@earthlink.net> wrote:
I'd like to see a proof of the claim (that the isomorphism of the subgraphs taking 1?>1, 2?>2, 4?>5, 5?>6 does not extend to an isomorphism G ?> G).
Without my taking a position on whether my first solution is valid, here's an alternative solution: The countably infinite vertex set consists, not of all integers, but of all rationals except 0, 1, and -1. Each vertex x is connected to every other vertex except -x and 1/x.