Theorem eufOLD 2273

Description: Obsolete proof of euf 2272 as of 30-Oct-2018. (Contributed by NM, 12-Aug-1993.) (Proof modification is discouraged.) (New usage is discouraged.)

Hypothesis

Ref	Expression
euf.1	|- F/ y ph

Assertion

Ref	Expression
eufOLD	|- ( E! x ph <-> E. y A. x ( ph <-> x = y ) )

Distinct variable group:   x, y

Allowed substitution hints:   ph( x, y)

Proof of Theorem eufOLD

Dummy variable z is distinct from all other variables.

Step	Hyp	Ref	Expression
1		df-eu 2266	. 2 |- ( E! x ph <-> E. z A. x ( ph <-> x = z ) )
2		euf.1	. . . . 5 |- F/ y ph
3		nfv 1674	. . . . 5 |- F/ y x = z
4	2, 3	nfbi 1872	. . . 4 |- F/ y ( ph <-> x = z )
5	4	nfal 1885	. . 3 |- F/ y A. x ( ph <-> x = z )
6		nfv 1674	. . . . 5 |- F/ z ph
7		nfv 1674	. . . . 5 |- F/ z x = y
8	6, 7	nfbi 1872	. . . 4 |- F/ z ( ph <-> x = y )
9	8	nfal 1885	. . 3 |- F/ z A. x ( ph <-> x = y )
10		equequ2 1739	. . . . 5 |- ( z = y -> ( x = z <-> x = y ) )
11	10	bibi2d 318	. . . 4 |- ( z = y -> ( ( ph <-> x = z ) <-> ( ph <-> x = y ) ) )
12	11	albidv 1680	. . 3 |- ( z = y -> ( A. x ( ph <-> x = z ) <-> A. x ( ph <-> x = y ) ) )
13	5, 9, 12	cbvex 1982	. 2 |- ( E. z A. x ( ph <-> x = z ) <-> E. y A. x ( ph <-> x = y ) )
14	1, 13	bitri 249	1 |- ( E! x ph <-> E. y A. x ( ph <-> x = y ) )

Syntax hints:   <-> wb 184   A.wal 1368   E.wex 1587   F/wnf 1590   E!weu 2262

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1592  ax-4 1603  ax-5 1671  ax-6 1710  ax-7 1730  ax-10 1777  ax-11 1782  ax-12 1794  ax-13 1955

This theorem depends on definitions:  df-bi 185  df-an 371  df-tru 1373  df-ex 1588  df-nf 1591  df-eu 2266

This theorem is referenced by: (None)