Theorem mtod 168

Description: Modus tollens deduction. (Contributed by NM, 3-Apr-1994.) (Proof shortened by Wolf Lammen, 11-Sep-2013.)

Hypotheses

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

Assertion

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

Proof of Theorem mtod

Step	Hyp	Ref	Expression
1		mtod.2	. 2 |- (ph -> (ps -> ch))
2		mtod.1	. . 3 |- (ph -> -. ch)
3	2	a1d 22	. 2 |- (ph -> (ps -> -. ch))
4	1, 3	pm2.65d 166	1 |- (ph -> -. ps)

Syntax hints:  -. wn 3   -> wi 4

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem is referenced by:  mtoi  169  mtbid  291  mtbird  292  mtand  640  mtord  641  ltfinasym  4460  lenltfin  4469  tfinltfin  4501  nnadjoin  4520  sfin111  4536  vfinncvntnn  4548  enprmaplem3  6078