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Theorem qexmid 1827
Description: Quantified "excluded middle." Exercise 9.2a of Boolos, p. 111, Computability and Logic. (Contributed by NM, 10-Dec-2000.)
Assertion
Ref Expression
qexmid  |-  E. x
( ph  ->  A. x ph )

Proof of Theorem qexmid
StepHypRef Expression
1 19.8a 1718 . 2  |-  ( A. x ph  ->  E. x A. x ph )
2119.35ri 1589 1  |-  E. x
( ph  ->  A. x ph )
Colors of variables: wff set class
Syntax hints:    -> wi 4   A.wal 1527   E.wex 1528
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1533  ax-5 1544  ax-17 1603  ax-9 1635  ax-8 1643  ax-11 1715
This theorem depends on definitions:  df-bi 177  df-an 360  df-ex 1529
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