Theorem fdmOLD

Description: Obsolete version of fdm as of 29-May-2024. (Contributed by NM, 2-Aug-1994) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	fdmOLD	⊢ ( 𝐹 : 𝐴 ⟶ 𝐵 → dom 𝐹 = 𝐴 )

Proof

Step	Hyp	Ref	Expression
1		ffn	⊢ ( 𝐹 : 𝐴 ⟶ 𝐵 → 𝐹 Fn 𝐴 )
2		fndm	⊢ ( 𝐹 Fn 𝐴 → dom 𝐹 = 𝐴 )
3	1 2	syl	⊢ ( 𝐹 : 𝐴 ⟶ 𝐵 → dom 𝐹 = 𝐴 )