User talk:DanChristensen

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Cheers! &mdash; Lord_Farin (talk) 18:53, 11 June 2013 (UTC)

Cantor-Bernstein-Schröder
If you want a challenge...

Prove the following in NBG theory without the choice, power set, infinity, or foundation axioms (not that you'll likely have any use for foundation here):

If $A$ and $B$ are classes and there are injective (class) functions $f: A \to B$ and $g:B \to A$, then there is a bijection $h: A \to B$. --Dfeuer (talk) 05:30, 17 June 2013 (UTC)