Theorem sb8eu 1961

Description: Variable substitution in unique existential 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 1466	. . . . 5 |- F/ w ( ph <-> x = z )
2	1	sb8 1784	. . . 4 |- ( A. x ( ph <-> x = z ) <-> A. w [ w / x ] ( ph <-> x = z ) )
3		sbbi 1881	. . . . . 6 |- ( [ w / x ] ( ph <-> x = z ) <-> ( [ w / x ] ph <-> [ w / x ] x = z ) )
4		sb8eu.1	. . . . . . . 8 |- F/ y ph
5	4	nfsb 1870	. . . . . . 7 |- F/ y [ w / x ] ph
6		equsb3 1873	. . . . . . . 8 |- ( [ w / x ] x = z <-> w = z )
7		nfv 1466	. . . . . . . 8 |- F/ y w = z
8	6, 7	nfxfr 1408	. . . . . . 7 |- F/ y [ w / x ] x = z
9	5, 8	nfbi 1526	. . . . . 6 |- F/ y ( [ w / x ] ph <-> [ w / x ] x = z )
10	3, 9	nfxfr 1408	. . . . 5 |- F/ y [ w / x ] ( ph <-> x = z )
11		nfv 1466	. . . . 5 |- F/ w [ y / x ] ( ph <-> x = z )
12		sbequ 1768	. . . . 5 |- ( w = y -> ( [ w / x ] ( ph <-> x = z ) <-> [ y / x ] ( ph <-> x = z ) ) )
13	10, 11, 12	cbval 1684	. . . 4 |- ( A. w [ w / x ] ( ph <-> x = z ) <-> A. y [ y / x ] ( ph <-> x = z ) )
14		equsb3 1873	. . . . . 6 |- ( [ y / x ] x = z <-> y = z )
15	14	sblbis 1882	. . . . 5 |- ( [ y / x ] ( ph <-> x = z ) <-> ( [ y / x ] ph <-> y = z ) )
16	15	albii 1404	. . . 4 |- ( A. y [ y / x ] ( ph <-> x = z ) <-> A. y ( [ y / x ] ph <-> y = z ) )
17	2, 13, 16	3bitri 204	. . 3 |- ( A. x ( ph <-> x = z ) <-> A. y ( [ y / x ] ph <-> y = z ) )
18	17	exbii 1541	. 2 |- ( E. z A. x ( ph <-> x = z ) <-> E. z A. y ( [ y / x ] ph <-> y = z ) )
19		df-eu 1951	. 2 |- ( E! x ph <-> E. z A. x ( ph <-> x = z ) )
20		df-eu 1951	. 2 |- ( E! y [ y / x ] ph <-> E. z A. y ( [ y / x ] ph <-> y = z ) )
21	18, 19, 20	3bitr4i 210	1 |- ( E! x ph <-> E! y [ y / x ] ph )

Syntax hints:   <-> wb 103   A.wal 1287   F/wnf 1394   E.wex 1426   [wsb 1692   E!weu 1948

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-io 665  ax-5 1381  ax-7 1382  ax-gen 1383  ax-ie1 1427  ax-ie2 1428  ax-8 1440  ax-10 1441  ax-11 1442  ax-i12 1443  ax-bndl 1444  ax-4 1445  ax-17 1464  ax-i9 1468  ax-ial 1472  ax-i5r 1473

This theorem depends on definitions:  df-bi 115  df-tru 1292  df-nf 1395  df-sb 1693  df-eu 1951

This theorem is referenced by:  sb8mo  1962  nfeud  1964  nfeu  1967  cbveu  1972  cbvreu  2588  acexmid  5633