Theorem sbexyz 1879

Description: Move existential quantifier in and out of substitution. Identical to sbex 1880 except that it has an additional distinct variable constraint on y and z. (Contributed by Jim Kingdon, 29-Dec-2017.)

Assertion

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

Distinct variable group:   x, y, z

Allowed substitution hints:   ph( x, y, z)

Proof of Theorem sbexyz

Step	Hyp	Ref	Expression
1		sb5 1767	. . 3 |- ( [ z / y ] E. x ph <-> E. y ( y = z /\ E. x ph ) )
2		exdistr 1787	. . 3 |- ( E. y E. x ( y = z /\ ph ) <-> E. y ( y = z /\ E. x ph ) )
3		excom 1554	. . 3 |- ( E. y E. x ( y = z /\ ph ) <-> E. x E. y ( y = z /\ ph ) )
4	1, 2, 3	3bitr2i 197	. 2 |- ( [ z / y ] E. x ph <-> E. x E. y ( y = z /\ ph ) )
5		sb5 1767	. . 3 |- ( [ z / y ] ph <-> E. y ( y = z /\ ph ) )
6	5	exbii 1496	. 2 |- ( E. x [ z / y ] ph <-> E. x E. y ( y = z /\ ph ) )
7	4, 6	bitr4i 176	1 |- ( [ z / y ] E. x ph <-> E. x [ z / y ] ph )

Syntax hints:   /\ wa 97   <-> wb 98   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:  sbex  1880