Theorem cbvexh 1769

Description: Rule used to change bound variables, using implicit substitition. (Contributed by NM, 5-Aug-1993.) (Revised by Mario Carneiro, 3-Feb-2015.)

Hypotheses

Ref	Expression
cbvexh.1	|- ( ph -> A. y ph )
cbvexh.2	|- ( ps -> A. x ps )
cbvexh.3	|- ( x = y -> ( ph <-> ps ) )

Assertion

Ref	Expression
cbvexh	|- ( E. x ph <-> E. y ps )

Proof of Theorem cbvexh

Step	Hyp	Ref	Expression
1		cbvexh.2	. . . 4 |- ( ps -> A. x ps )
2	1	hbex 1650	. . 3 |- ( E. y ps -> A. x E. y ps )
3		cbvexh.1	. . . . 5 |- ( ph -> A. y ph )
4		cbvexh.3	. . . . . . 7 |- ( x = y -> ( ph <-> ps ) )
5	4	bicomd 141	. . . . . 6 |- ( x = y -> ( ps <-> ph ) )
6	5	equcoms 1722	. . . . 5 |- ( y = x -> ( ps <-> ph ) )
7	3, 6	equsex 1742	. . . 4 |- ( E. y ( y = x /\ ps ) <-> ph )
8		simpr 110	. . . . 5 |- ( ( y = x /\ ps ) -> ps )
9	8	eximi 1614	. . . 4 |- ( E. y ( y = x /\ ps ) -> E. y ps )
10	7, 9	sylbir 135	. . 3 |- ( ph -> E. y ps )
11	2, 10	exlimih 1607	. 2 |- ( E. x ph -> E. y ps )
12	3	hbex 1650	. . 3 |- ( E. x ph -> A. y E. x ph )
13	1, 4	equsex 1742	. . . 4 |- ( E. x ( x = y /\ ph ) <-> ps )
14		simpr 110	. . . . 5 |- ( ( x = y /\ ph ) -> ph )
15	14	eximi 1614	. . . 4 |- ( E. x ( x = y /\ ph ) -> E. x ph )
16	13, 15	sylbir 135	. . 3 |- ( ps -> E. x ph )
17	12, 16	exlimih 1607	. 2 |- ( E. y ps -> E. x ph )
18	11, 17	impbii 126	1 |- ( E. x ph <-> E. y ps )

Syntax hints:   -> wi 4   /\ wa 104   <-> wb 105   A.wal 1362   = wceq 1364   E.wex 1506

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-5 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548

This theorem depends on definitions:  df-bi 117

This theorem is referenced by:  cbvex  1770  sb8eh  1869  cbvexv  1933  euf  2050  mopick  2123