Theorem mo2 2274

Description: Alternate definition of "at most one." (Contributed by NM, 8-Mar-1995.) Restrict dummy variable z. (Revised by Wolf Lammen, 28-May-2019.)

Hypothesis

Ref	Expression
mo2.1	|- F/ y ph

Assertion

Ref	Expression
mo2	|- ( E* x ph <-> E. y A. x ( ph -> x = y ) )

Distinct variable group:   x, y

Allowed substitution hints:   ph( x, y)

Proof of Theorem mo2

Dummy variable z is distinct from all other variables.

Step	Hyp	Ref	Expression
1		mo2v 2269	. 2 |- ( E* x ph <-> E. z A. x ( ph -> x = z ) )
2		mo2.1	. . . . 5 |- F/ y ph
3		nfv 1674	. . . . 5 |- F/ y x = z
4	2, 3	nfim 1858	. . . 4 |- F/ y ( ph -> x = z )
5	4	nfal 1885	. . 3 |- F/ y A. x ( ph -> x = z )
6		nfv 1674	. . 3 |- F/ z A. x ( ph -> x = y )
7		equequ2 1739	. . . . 5 |- ( z = y -> ( x = z <-> x = y ) )
8	7	imbi2d 316	. . . 4 |- ( z = y -> ( ( ph -> x = z ) <-> ( ph -> x = y ) ) )
9	8	albidv 1680	. . 3 |- ( z = y -> ( A. x ( ph -> x = z ) <-> A. x ( ph -> x = y ) ) )
10	5, 6, 9	cbvex 1982	. 2 |- ( E. z A. x ( ph -> x = z ) <-> E. y A. x ( ph -> x = y ) )
11	1, 10	bitri 249	1 |- ( E* x ph <-> E. y A. x ( ph -> x = y ) )

Syntax hints:   -> wi 4   <-> wb 184   A.wal 1368   E.wex 1587   F/wnf 1590   E*wmo 2263

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-ex 1588  df-nf 1591  df-eu 2266  df-mo 2267

This theorem is referenced by:  mo3  2307  mo3OLD  2308  mo  2309  mo3OLDOLD  2310  eu5OLD  2318  morimvOLD  2331  moanimOLD  2342  rmo2  3391  nmo  26041  bj-eu3f  32700