Theorem pm2.25dc 888

Description: Elimination of disjunction based on a disjunction, for a decidable proposition. Based on theorem *2.25 of [WhiteheadRussell] p. 104. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.25dc	|- (DECID ph -> ( ph \/ ( ( ph \/ ps ) -> ps ) ) )

Proof of Theorem pm2.25dc

Step	Hyp	Ref	Expression
1		df-dc 830	. 2 |- (DECID ph <-> ( ph \/ -. ph ) )
2		orel1 720	. . 3 |- ( -. ph -> ( ( ph \/ ps ) -> ps ) )
3	2	orim2i 756	. 2 |- ( ( ph \/ -. ph ) -> ( ph \/ ( ( ph \/ ps ) -> ps ) ) )
4	1, 3	sylbi 120	1 |- (DECID ph -> ( ph \/ ( ( ph \/ ps ) -> ps ) ) )

Syntax hints:   -. wn 3   -> wi 4   \/ wo 703  DECID wdc 829

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in2 610  ax-io 704

This theorem depends on definitions:  df-bi 116  df-dc 830

This theorem is referenced by: (None)