Metamath Proof Explorer

Theorem pm2.1

Description: Theorem *2.1 of WhiteheadRussell p. 101. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 23-Nov-2012)

Ref Expression
Assertion pm2.1 
|- ( -. ph \/ ph )

Proof

Step Hyp Ref Expression
1 id 
 |-  ( ph -> ph )
2 1 imori 
 |-  ( -. ph \/ ph )