Theorem cbvexh 1743

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 1624	. . 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 140	. . . . . 6 |- ( x = y -> ( ps <-> ph ) )
6	5	equcoms 1696	. . . . 5 |- ( y = x -> ( ps <-> ph ) )
7	3, 6	equsex 1716	. . . 4 |- ( E. y ( y = x /\ ps ) <-> ph )
8		simpr 109	. . . . 5 |- ( ( y = x /\ ps ) -> ps )
9	8	eximi 1588	. . . 4 |- ( E. y ( y = x /\ ps ) -> E. y ps )
10	7, 9	sylbir 134	. . 3 |- ( ph -> E. y ps )
11	2, 10	exlimih 1581	. 2 |- ( E. x ph -> E. y ps )
12	3	hbex 1624	. . 3 |- ( E. x ph -> A. y E. x ph )
13	1, 4	equsex 1716	. . . 4 |- ( E. x ( x = y /\ ph ) <-> ps )
14		simpr 109	. . . . 5 |- ( ( x = y /\ ph ) -> ph )
15	14	eximi 1588	. . . 4 |- ( E. x ( x = y /\ ph ) -> E. x ph )
16	13, 15	sylbir 134	. . 3 |- ( ps -> E. x ph )
17	12, 16	exlimih 1581	. 2 |- ( E. y ps -> E. x ph )
18	11, 17	impbii 125	1 |- ( E. x ph <-> E. y ps )

Syntax hints:   -> wi 4   /\ wa 103   <-> wb 104   A.wal 1341   = wceq 1343   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-5 1435  ax-7 1436  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-8 1492  ax-4 1498  ax-17 1514  ax-i9 1518  ax-ial 1522

This theorem depends on definitions:  df-bi 116

This theorem is referenced by:  cbvex  1744  sb8eh  1843  cbvexv  1906  euf  2019  mopick  2092