In fact you don't even need to do that. In fact I prefer to use just X or something so as to avoid the misleading language of mapping / relation theory.
See what I did in:
Exists Bijection to a Disjoint Set - ProofWiki
In fact you don't even need to do that. In fact I prefer to use just X or something so as to avoid the misleading language of mapping / relation theory.
See what I did in:
Exists Bijection to a Disjoint Set - ProofWiki