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Theorem nbbn 349
Description: Move negation outside of biconditional. Compare Theorem *5.18 of [WhiteheadRussell] p. 124. (Contributed by NM, 27-Jun-2002.) (Proof shortened by Wolf Lammen, 20-Sep-2013.)
Assertion
Ref Expression
nbbn  |-  ( ( -.  ph  <->  ps )  <->  -.  ( ph 
<->  ps ) )

Proof of Theorem nbbn
StepHypRef Expression
1 xor3 348 . 2  |-  ( -.  ( ph  <->  ps )  <->  (
ph 
<->  -.  ps ) )
2 con2bi 320 . 2  |-  ( (
ph 
<->  -.  ps )  <->  ( ps  <->  -. 
ph ) )
3 bicom 193 . 2  |-  ( ( ps  <->  -.  ph )  <->  ( -.  ph  <->  ps ) )
41, 2, 33bitrri 265 1  |-  ( ( -.  ph  <->  ps )  <->  -.  ( ph 
<->  ps ) )
Colors of variables: wff set class
Syntax hints:   -. wn 5    <-> wb 178
This theorem is referenced by:  biass  350  pclem6  901  xorass  1304  xorneg1  1307  trubifal  1347  hadbi  1383  mpto2  1529  canth  6225  qextltlem  10460  onint1  24228
This theorem was proved from axioms:  ax-1 7  ax-2 8  ax-3 9  ax-mp 10
This theorem depends on definitions:  df-bi 179
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