Theorem fofn

Description: An onto mapping is a function on its domain. (Contributed by NM, 16-Dec-2008)

	Ref	Expression
Assertion	fofn	$$⊢F:A\underset{onto}{⟶}B\to FFnA$$

Proof

Step	Hyp	Ref	Expression
1		fof	$$⊢F:A\underset{onto}{⟶}B\to F:A⟶B$$
2	1	ffnd	$$⊢F:A\underset{onto}{⟶}B\to FFnA$$