Metamath Proof Explorer


Theorem 19.29r

Description: Variation of 19.29 . (Contributed by NM, 18-Aug-1993) (Proof shortened by Wolf Lammen, 12-Nov-2020)

Ref Expression
Assertion 19.29r xφxψxφψ

Proof

Step Hyp Ref Expression
1 pm3.21 ψφφψ
2 1 aleximi xψxφxφψ
3 2 impcom xφxψxφψ