Theorem exalim 1391

Description: One direction of a classical definition of existential quantification. One direction of Definition of [Margaris] p. 49. For a decidable proposition, this is an equivalence, as seen as dfexdc 1390. (Contributed by Jim Kingdon, 29-Jul-2018.)

Assertion

Ref	Expression
exalim	|- ( E. x ph -> -. A. x -. ph )

Proof of Theorem exalim

Step	Hyp	Ref	Expression
1		alnex 1388	. . 3 |- ( A. x -. ph <-> -. E. x ph )
2	1	biimpi 113	. 2 |- ( A. x -. ph -> -. E. x ph )
3	2	con2i 557	1 |- ( E. x ph -> -. A. x -. ph )

Syntax hints:   -. wn 3   -> wi 4   A.wal 1241   E.wex 1381

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545  ax-5 1336  ax-gen 1338  ax-ie2 1383

This theorem depends on definitions:  df-bi 110  df-tru 1246  df-fal 1249

This theorem is referenced by:  n0rf  3233  ax9vsep  3880