Theorem pm5.19 349

Description: Theorem *5.19 of [WhiteheadRussell] p. 124. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm5.19	|- -. (ph <-> -. ph)

Proof of Theorem pm5.19

Step	Hyp	Ref	Expression
1		biid 227	. 2 |- (ph <-> ph)
2		pm5.18 345	. 2 |- ((ph <-> ph) <-> -. (ph <-> -. ph))
3	1, 2	mpbi 199	1 |- -. (ph <-> -. ph)

This proof depends on syntax axioms:  -. wn 3   <-> wb 176

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This proof depends on definitions:  df-bi 177

This theorem is used by:  ru  3046  necompl  3545  nenpw1pwlem2  6086