Metamath Proof Explorer


Theorem bi2.04

Description: Logical equivalence of commuted antecedents. Part of Theorem *4.87 of WhiteheadRussell p. 122. (Contributed by NM, 11-May-1993)

Ref Expression
Assertion bi2.04 φψχψφχ

Proof

Step Hyp Ref Expression
1 pm2.04 φψχψφχ
2 pm2.04 ψφχφψχ
3 1 2 impbii φψχψφχ