Theorem alexim 1669

Description: One direction of theorem 19.6 of [Margaris] p. 89. The converse holds given a decidability condition, as seen at alexdc 1643. (Contributed by Jim Kingdon, 2-Jul-2018.)

Assertion

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

Proof of Theorem alexim

Step	Hyp	Ref	Expression
1		pm2.24 622	. . . . 5 |- ( ph -> ( -. ph -> F. ) )
2	1	alimi 1479	. . . 4 |- ( A. x ph -> A. x ( -. ph -> F. ) )
3		exim 1623	. . . 4 |- ( A. x ( -. ph -> F. ) -> ( E. x -. ph -> E. x F. ) )
4	2, 3	syl 14	. . 3 |- ( A. x ph -> ( E. x -. ph -> E. x F. ) )
5		nfv 1552	. . . 4 |- F/ x F.
6	5	19.9 1668	. . 3 |- ( E. x F. <-> F. )
7	4, 6	imbitrdi 161	. 2 |- ( A. x ph -> ( E. x -. ph -> F. ) )
8		dfnot 1391	. 2 |- ( -. E. x -. ph <-> ( E. x -. ph -> F. ) )
9	7, 8	sylibr 134	1 |- ( A. x ph -> -. E. x -. ph )

Syntax hints:   -. wn 3   -> wi 4   A.wal 1371   F. wfal 1378   E.wex 1516

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 615  ax-in2 616  ax-5 1471  ax-gen 1473  ax-ie1 1517  ax-ie2 1518  ax-4 1534  ax-17 1550  ax-ial 1558

This theorem depends on definitions:  df-bi 117  df-tru 1376  df-fal 1379  df-nf 1485

This theorem is referenced by:  exnalim  1670  exists2  2153