Metamath Proof Explorer

Theorem unexgOLD

Description: Obsolete proof of unexg as of 21-Jul-2025. (Contributed by NM, 18-Sep-2006) (Proof modification is discouraged.) (New usage is discouraged.)

Ref Expression
Assertion unexgOLD ⊢ A ∈ V ∧ B ∈ W → A ∪ B ∈ V

Proof

Step Hyp Ref Expression
1 elex ⊢ A ∈ V → A ∈ V
2 elex ⊢ B ∈ W → B ∈ V
3 unexb ⊢ A ∈ V ∧ B ∈ V ↔ A ∪ B ∈ V
4 3 biimpi ⊢ A ∈ V ∧ B ∈ V → A ∪ B ∈ V
5 1 2 4 syl2an ⊢ A ∈ V ∧ B ∈ W → A ∪ B ∈ V