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Theorem mpto2 1524
Description: Modus ponendo tollens 2, one of the "indemonstrables" in Stoic logic. Note that this uses exclusive-or  \/_. See rule 2 on [Lopez-Astorga] p. 12 , rule 4 on [Sanford] p. 39 and rule A4 in [Hitchcock] p. 5 . (Contributed by David A. Wheeler, 3-Jul-2016.)
Hypotheses
Ref Expression
mpto2.1  |-  ph
mpto2.2  |-  ( ph \/_ ps )
Assertion
Ref Expression
mpto2  |-  -.  ps

Proof of Theorem mpto2
StepHypRef Expression
1 mpto2.1 . 2  |-  ph
2 mpto2.2 . . . . 5  |-  ( ph \/_ ps )
3 df-xor 1296 . . . . 5  |-  ( (
ph \/_ ps )  <->  -.  ( ph 
<->  ps ) )
42, 3mpbi 199 . . . 4  |-  -.  ( ph 
<->  ps )
5 nbbn 347 . . . 4  |-  ( ( -.  ph  <->  ps )  <->  -.  ( ph 
<->  ps ) )
64, 5mpbir 200 . . 3  |-  ( -. 
ph 
<->  ps )
76con1bii 321 . 2  |-  ( -. 
ps 
<-> 
ph )
81, 7mpbir 200 1  |-  -.  ps
Colors of variables: wff set class
Syntax hints:   -. wn 3    <-> wb 176   \/_wxo 1295
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
This theorem depends on definitions:  df-bi 177  df-xor 1296
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