Theorem sb8eh 1735

Description: Substitution of variable in existential quantifier. (Contributed by NM, 12-Aug-1993.) (Proof rewritten by Jim Kingdon, 15-Jan-2018.)

Hypothesis

Ref	Expression
sb8eh.1	|- ( ph -> A. y ph )

Assertion

Ref	Expression
sb8eh	|- ( E. x ph <-> E. y [ y / x ] ph )

Proof of Theorem sb8eh

Step	Hyp	Ref	Expression
1		sb8eh.1	. 2 |- ( ph -> A. y ph )
2	1	hbsb3 1689	. 2 |- ( [ y / x ] ph -> A. x [ y / x ] ph )
3		sbequ12 1654	. 2 |- ( x = y -> ( ph <-> [ y / x ] ph ) )
4	1, 2, 3	cbvexh 1638	1 |- ( E. x ph <-> E. y [ y / x ] ph )

Syntax hints:   -> wi 4   <-> wb 98   A.wal 1241   E.wex 1381   [wsb 1645

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-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-11 1397  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427

This theorem depends on definitions:  df-bi 110  df-sb 1646

This theorem is referenced by:  exsb  1884