Metamath Proof Explorer


Theorem pm10.253

Description: Theorem *10.253 in WhiteheadRussell p. 149. (Contributed by Andrew Salmon, 17-Jun-2011)

Ref Expression
Assertion pm10.253 ¬xφx¬φ

Proof

Step Hyp Ref Expression
1 alex xφ¬x¬φ
2 1 bicomi ¬x¬φxφ
3 2 con1bii ¬xφx¬φ