Theorem axc4 1938

Description: Show that the original axiom ax-c4 32456 can be derived from ax-4 1682 and others. See ax4 32466 for the rederivation of ax-4 1682 from ax-c4 32456.

Part of the proof is based on the proof of Lemma 22 of [Monk2] p. 114. (Contributed by NM, 21-May-2008.) (Proof modification is discouraged.)

Assertion

Ref	Expression
axc4	|- ( A. x ( A. x ph -> ps ) -> ( A. x ph -> A. x ps ) )

Proof of Theorem axc4

Step	Hyp	Ref	Expression
1		sp 1937	. . . 4 |- ( A. x -. A. x ph -> -. A. x ph )
2	1	con2i 124	. . 3 |- ( A. x ph -> -. A. x -. A. x ph )
3		hbn1 1916	. . 3 |- ( -. A. x -. A. x ph -> A. x -. A. x -. A. x ph )
4		hbn1 1916	. . . . 5 |- ( -. A. x ph -> A. x -. A. x ph )
5	4	con1i 133	. . . 4 |- ( -. A. x -. A. x ph -> A. x ph )
6	5	alimi 1684	. . 3 |- ( A. x -. A. x -. A. x ph -> A. x A. x ph )
7	2, 3, 6	3syl 18	. 2 |- ( A. x ph -> A. x A. x ph )
8		alim 1683	. 2 |- ( A. x ( A. x ph -> ps ) -> ( A. x A. x ph -> A. x ps ) )
9	7, 8	syl5 33	1 |- ( A. x ( A. x ph -> ps ) -> ( A. x ph -> A. x ps ) )

Syntax hints:   -. wn 3   -> wi 4   A.wal 1442

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1669  ax-4 1682  ax-5 1758  ax-6 1805  ax-7 1851  ax-10 1915  ax-12 1933

This theorem depends on definitions:  df-bi 189  df-an 373  df-ex 1664

This theorem is referenced by:  axc5c4c711  36752