Theorem pm2.521dcALT 875

Description: Alternate proof of pm2.521dc 874. (Contributed by Jim Kingdon, 5-May-2018.) (Proof modification is discouraged.) (New usage is discouraged.)

Assertion

Ref	Expression
pm2.521dcALT	|- (DECID ph -> ( -. ( ph -> ps ) -> ( ps -> ph ) ) )

Proof of Theorem pm2.521dcALT

Step	Hyp	Ref	Expression
1		pm2.52 660	. 2 |- ( -. ( ph -> ps ) -> ( -. ph -> -. ps ) )
2		condc 858	. 2 |- (DECID ph -> ( ( -. ph -> -. ps ) -> ( ps -> ph ) ) )
3	1, 2	syl5 32	1 |- (DECID ph -> ( -. ( ph -> ps ) -> ( ps -> ph ) ) )

Syntax hints:   -. wn 3   -> wi 4  DECID wdc 839

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 617  ax-in2 618  ax-io 714

This theorem depends on definitions:  df-bi 117  df-stab 836  df-dc 840

This theorem is referenced by: (None)