Metamath Proof Explorer


Theorem pm5.61

Description: Theorem *5.61 of WhiteheadRussell p. 125. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 30-Jun-2013)

Ref Expression
Assertion pm5.61 φ ψ ¬ ψ φ ¬ ψ

Proof

Step Hyp Ref Expression
1 orel2 ¬ ψ φ ψ φ
2 orc φ φ ψ
3 1 2 impbid1 ¬ ψ φ ψ φ
4 3 pm5.32ri φ ψ ¬ ψ φ ¬ ψ