Theorem pm4.8 162

Description: Theorem *4.8 of [WhiteheadRussell] p. 122.

Assertion

Ref	Expression
pm4.8	|- ((ph -> -. ph) <-> -. ph)

Proof of Theorem pm4.8

Step	Hyp	Ref	Expression
1		pm2.01 88	. 2 |- ((ph -> -. ph) -> -. ph)
2		ax-1 4	. 2 |- (-. ph -> (ph -> -. ph))
3	1, 2	impbi 157	1 |- ((ph -> -. ph) <-> -. ph)

Syntax hints:  -. wn 2   -> wi 3   <-> wb 146

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7

This theorem depends on definitions:  df-bi 147

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