Theorem mt2d 111

Description: Modus tollens deduction.

Hypotheses

Ref	Expression
mt2d.1	|- (ph -> ch)
mt2d.2	|- (ph -> (ps -> -. ch))

Assertion

Ref	Expression
mt2d	|- (ph -> -. ps)

Proof of Theorem mt2d

Step	Hyp	Ref	Expression
1		mt2d.1	. 2 |- (ph -> ch)
2		mt2d.2	. . 3 |- (ph -> (ps -> -. ch))
3	2	con2d 91	. 2 |- (ph -> (ch -> -. ps))
4	1, 3	mpd 26	1 |- (ph -> -. ps)

Syntax hints:  -. wn 2   -> wi 3

This theorem is referenced by:  nn0ltp1let 6127  recnzt 6191

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

Copyright terms: Public domain