Theorem sb8eu 1913

Description: Variable substitution in uniqueness quantifier. (Contributed by NM, 7-Aug-1994.) (Revised by Mario Carneiro, 7-Oct-2016.)

Hypothesis

Ref	Expression
sb8eu.1	|- F/ y ph

Assertion

Ref	Expression
sb8eu	|- ( E! x ph <-> E! y [ y / x ] ph )

Proof of Theorem sb8eu

Dummy variables w z are mutually distinct and distinct from all other variables.

Step	Hyp	Ref	Expression
1		nfv 1421	. . . . 5 |- F/ w ( ph <-> x = z )
2	1	sb8 1736	. . . 4 |- ( A. x ( ph <-> x = z ) <-> A. w [ w / x ] ( ph <-> x = z ) )
3		sbbi 1833	. . . . . 6 |- ( [ w / x ] ( ph <-> x = z ) <-> ( [ w / x ] ph <-> [ w / x ] x = z ) )
4		sb8eu.1	. . . . . . . 8 |- F/ y ph
5	4	nfsb 1822	. . . . . . 7 |- F/ y [ w / x ] ph
6		equsb3 1825	. . . . . . . 8 |- ( [ w / x ] x = z <-> w = z )
7		nfv 1421	. . . . . . . 8 |- F/ y w = z
8	6, 7	nfxfr 1363	. . . . . . 7 |- F/ y [ w / x ] x = z
9	5, 8	nfbi 1481	. . . . . 6 |- F/ y ( [ w / x ] ph <-> [ w / x ] x = z )
10	3, 9	nfxfr 1363	. . . . 5 |- F/ y [ w / x ] ( ph <-> x = z )
11		nfv 1421	. . . . 5 |- F/ w [ y / x ] ( ph <-> x = z )
12		sbequ 1721	. . . . 5 |- ( w = y -> ( [ w / x ] ( ph <-> x = z ) <-> [ y / x ] ( ph <-> x = z ) ) )
13	10, 11, 12	cbval 1637	. . . 4 |- ( A. w [ w / x ] ( ph <-> x = z ) <-> A. y [ y / x ] ( ph <-> x = z ) )
14		equsb3 1825	. . . . . 6 |- ( [ y / x ] x = z <-> y = z )
15	14	sblbis 1834	. . . . 5 |- ( [ y / x ] ( ph <-> x = z ) <-> ( [ y / x ] ph <-> y = z ) )
16	15	albii 1359	. . . 4 |- ( A. y [ y / x ] ( ph <-> x = z ) <-> A. y ( [ y / x ] ph <-> y = z ) )
17	2, 13, 16	3bitri 195	. . 3 |- ( A. x ( ph <-> x = z ) <-> A. y ( [ y / x ] ph <-> y = z ) )
18	17	exbii 1496	. 2 |- ( E. z A. x ( ph <-> x = z ) <-> E. z A. y ( [ y / x ] ph <-> y = z ) )
19		df-eu 1903	. 2 |- ( E! x ph <-> E. z A. x ( ph <-> x = z ) )
20		df-eu 1903	. 2 |- ( E! y [ y / x ] ph <-> E. z A. y ( [ y / x ] ph <-> y = z ) )
21	18, 19, 20	3bitr4i 201	1 |- ( E! x ph <-> E! y [ y / x ] ph )

Syntax hints:   <-> wb 98   A.wal 1241   F/wnf 1349   E.wex 1381   [wsb 1645   E!weu 1900

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-io 630  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-10 1396  ax-11 1397  ax-i12 1398  ax-bndl 1399  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427  ax-i5r 1428

This theorem depends on definitions:  df-bi 110  df-tru 1246  df-nf 1350  df-sb 1646  df-eu 1903

This theorem is referenced by:  sb8mo  1914  nfeud  1916  nfeu  1919  cbveu  1924  cbvreu  2531  acexmid  5511