Theorem pm3.14 743

Description: Theorem *3.14 of [WhiteheadRussell] p. 111. One direction of De Morgan's law). The biconditional holds for decidable propositions as seen at ianordc 889. The converse holds for decidable propositions, as seen at pm3.13dc 949. (Contributed by NM, 3-Jan-2005.) (Revised by Mario Carneiro, 31-Jan-2015.)

Assertion

Ref	Expression
pm3.14	|- ( ( -. ph \/ -. ps ) -> -. ( ph /\ ps ) )

Proof of Theorem pm3.14

Step	Hyp	Ref	Expression
1		simpl 108	. . 3 |- ( ( ph /\ ps ) -> ph )
2	1	con3i 622	. 2 |- ( -. ph -> -. ( ph /\ ps ) )
3		simpr 109	. . 3 |- ( ( ph /\ ps ) -> ps )
4	3	con3i 622	. 2 |- ( -. ps -> -. ( ph /\ ps ) )
5	2, 4	jaoi 706	1 |- ( ( -. ph \/ -. ps ) -> -. ( ph /\ ps ) )

Syntax hints:   -. wn 3   -> wi 4   /\ wa 103   \/ wo 698

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-in1 604  ax-in2 605  ax-io 699

This theorem depends on definitions:  df-bi 116

This theorem is referenced by:  pm3.1  744  xoranor  1367  difindiss  3376