Metamath Proof Explorer


Theorem rexcom

Description: Commutation of restricted existential quantifiers. (Contributed by NM, 19-Nov-1995) (Revised by Mario Carneiro, 14-Oct-2016) (Proof shortened by BJ, 26-Aug-2023) (Proof shortened by Wolf Lammen, 8-Dec-2024)

Ref Expression
Assertion rexcom x A y B φ y B x A φ

Proof

Step Hyp Ref Expression
1 ralcom x A y B ¬ φ y B x A ¬ φ
2 ralnex2 x A y B ¬ φ ¬ x A y B φ
3 ralnex2 y B x A ¬ φ ¬ y B x A φ
4 1 2 3 3bitr3i ¬ x A y B φ ¬ y B x A φ
5 4 con4bii x A y B φ y B x A φ