Theorem brdom2g

Description: Dominance relation. This variation of brdomg does not require the Axiom of Union. (Contributed by NM, 15-Jun-1998) Extract from a subproof of brdomg . (Revised by BTernaryTau, 29-Nov-2024)

	Ref	Expression
Assertion	brdom2g	$$⊢\left(A\in V\wedge B\in W\right)\to \left(A\preccurlyeq B\leftrightarrow \exists ff:A\underset{1-1}{⟶}B\right)$$

Proof

Step	Hyp	Ref	Expression
1		f1eq2	$$⊢x=A\to \left(f:x\underset{1-1}{⟶}y\leftrightarrow f:A\underset{1-1}{⟶}y\right)$$
2	1	exbidv	$$⊢x=A\to \left(\exists ff:x\underset{1-1}{⟶}y\leftrightarrow \exists ff:A\underset{1-1}{⟶}y\right)$$
3		f1eq3	$$⊢y=B\to \left(f:A\underset{1-1}{⟶}y\leftrightarrow f:A\underset{1-1}{⟶}B\right)$$
4	3	exbidv	$$⊢y=B\to \left(\exists ff:A\underset{1-1}{⟶}y\leftrightarrow \exists ff:A\underset{1-1}{⟶}B\right)$$
5		df-dom	$$⊢\preccurlyeq =\left\{⟨x,y⟩|\exists ff:x\underset{1-1}{⟶}y\right\}$$
6	2 4 5	brabg	$$⊢\left(A\in V\wedge B\in W\right)\to \left(A\preccurlyeq B\leftrightarrow \exists ff:A\underset{1-1}{⟶}B\right)$$