Metamath Proof Explorer


Theorem 19.21vv

Description: Compare Theorem *11.3 in WhiteheadRussell p. 161. Special case of theorem 19.21 of Margaris p. 90 with two quantifiers. See 19.21v . (Contributed by Andrew Salmon, 24-May-2011)

Ref Expression
Assertion 19.21vv xyψφψxyφ

Proof

Step Hyp Ref Expression
1 19.21v yψφψyφ
2 1 albii xyψφxψyφ
3 19.21v xψyφψxyφ
4 2 3 bitri xyψφψxyφ