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Theorem alex 1578
Description: Theorem 19.6 of [Margaris] p. 89. (Contributed by NM, 5-Aug-1993.)
Assertion
Ref Expression
alex  |-  ( A. x ph  <->  -.  E. x  -.  ph )

Proof of Theorem alex
StepHypRef Expression
1 notnot 283 . . 3  |-  ( ph  <->  -. 
-.  ph )
21albii 1572 . 2  |-  ( A. x ph  <->  A. x  -.  -.  ph )
3 alnex 1549 . 2  |-  ( A. x  -.  -.  ph  <->  -.  E. x  -.  ph )
42, 3bitri 241 1  |-  ( A. x ph  <->  -.  E. x  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    <-> wb 177   A.wal 1546   E.wex 1547
This theorem is referenced by:  2nalexn  1579  exnal  1580  19.3v  1673  sp  1759  hba1  1800  exists2  2352  pm10.253  27433  vk15.4j  28331  vk15.4jVD  28744
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1552  ax-5 1563
This theorem depends on definitions:  df-bi 178  df-ex 1548
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