Theorem brdomiOLD

Description: Obsolete version of brdomi as of 29-Nov-2024. (Contributed by Mario Carneiro, 26-Apr-2015) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	brdomiOLD	⊢ ( 𝐴 ≼ 𝐵 → ∃ 𝑓 𝑓 : 𝐴 –1-1→ 𝐵 )

Proof

Step	Hyp	Ref	Expression
1		reldom	⊢ Rel ≼
2	1	brrelex2i	⊢ ( 𝐴 ≼ 𝐵 → 𝐵 ∈ V )
3		brdomg	⊢ ( 𝐵 ∈ V → ( 𝐴 ≼ 𝐵 ↔ ∃ 𝑓 𝑓 : 𝐴 –1-1→ 𝐵 ) )
4	2 3	syl	⊢ ( 𝐴 ≼ 𝐵 → ( 𝐴 ≼ 𝐵 ↔ ∃ 𝑓 𝑓 : 𝐴 –1-1→ 𝐵 ) )
5	4	ibi	⊢ ( 𝐴 ≼ 𝐵 → ∃ 𝑓 𝑓 : 𝐴 –1-1→ 𝐵 )