Theorem mt2d 625

Description: Modus tollens deduction. (Contributed by NM, 4-Jul-1994.)

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 624	. 2 |- ( ph -> ( ch -> -. ps ) )
4	1, 3	mpd 13	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-in1 614  ax-in2 615

This theorem is referenced by:  nsyl3  626  mt2i  644  en2lp  4553  recnz  9344  xnn0dcle  9800  fznuz  10099  uznfz  10100  pcadd  12333  oddennn  12387