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Theorem nnal 1637
Description: The double negation of a universal quantification implies the universal quantification of the double negation. (Contributed by BJ, 24-Nov-2023.)
Assertion
Ref Expression
nnal  |-  ( -. 
-.  A. x ph  ->  A. x  -.  -.  ph )

Proof of Theorem nnal
StepHypRef Expression
1 exnalim 1634 . . 3  |-  ( E. x  -.  ph  ->  -. 
A. x ph )
21con3i 622 . 2  |-  ( -. 
-.  A. x ph  ->  -. 
E. x  -.  ph )
3 alnex 1487 . 2  |-  ( A. x  -.  -.  ph  <->  -.  E. x  -.  ph )
42, 3sylibr 133 1  |-  ( -. 
-.  A. x ph  ->  A. x  -.  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4   A.wal 1341   E.wex 1480
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605  ax-5 1435  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-4 1498  ax-17 1514  ax-ial 1522
This theorem depends on definitions:  df-bi 116  df-tru 1346  df-fal 1349  df-nf 1449
This theorem is referenced by:  bj-stal  13630
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