Metamath Proof Explorer


Theorem fodom

Description: An onto function implies dominance of domain over range. (Contributed by NM, 23-Jul-2004)

Ref Expression
Hypothesis fodom.1 A V
Assertion fodom F : A onto B B A

Proof

Step Hyp Ref Expression
1 fodom.1 A V
2 fodomg A V F : A onto B B A
3 1 2 ax-mp F : A onto B B A