Theorem fndm

Description: The domain of a function. (Contributed by NM, 2-Aug-1994)

	Ref	Expression
Assertion	fndm	⊢ ( 𝐹 Fn 𝐴 → dom 𝐹 = 𝐴 )

Proof

Step	Hyp	Ref	Expression
1		df-fn	⊢ ( 𝐹 Fn 𝐴 ↔ ( Fun 𝐹 ∧ dom 𝐹 = 𝐴 ) )
2	1	simprbi	⊢ ( 𝐹 Fn 𝐴 → dom 𝐹 = 𝐴 )