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Theorem mo2 2318
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.
StepHypRef Expression
1 mo2v 2316 . 2  |-  ( E* x ph  <->  E. z A. x ( ph  ->  x  =  z ) )
2 mo2.1 . . . . 5  |-  F/ y
ph
3 nfv 1771 . . . . 5  |-  F/ y  x  =  z
42, 3nfim 2013 . . . 4  |-  F/ y ( ph  ->  x  =  z )
54nfal 2040 . . 3  |-  F/ y A. x ( ph  ->  x  =  z )
6 nfv 1771 . . 3  |-  F/ z A. x ( ph  ->  x  =  y )
7 equequ2 1878 . . . . 5  |-  ( z  =  y  ->  (
x  =  z  <->  x  =  y ) )
87imbi2d 322 . . . 4  |-  ( z  =  y  ->  (
( ph  ->  x  =  z )  <->  ( ph  ->  x  =  y ) ) )
98albidv 1777 . . 3  |-  ( z  =  y  ->  ( A. x ( ph  ->  x  =  z )  <->  A. x
( ph  ->  x  =  y ) ) )
105, 6, 9cbvex 2125 . 2  |-  ( E. z A. x (
ph  ->  x  =  z )  <->  E. y A. x
( ph  ->  x  =  y ) )
111, 10bitri 257 1  |-  ( E* x ph  <->  E. y A. x ( ph  ->  x  =  y ) )
Colors of variables: wff setvar class
Syntax hints:    -> wi 4    <-> wb 189   A.wal 1452   E.wex 1673   F/wnf 1677   E*wmo 2310
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1679  ax-4 1692  ax-5 1768  ax-6 1815  ax-7 1861  ax-10 1925  ax-11 1930  ax-12 1943  ax-13 2101
This theorem depends on definitions:  df-bi 190  df-an 377  df-ex 1674  df-nf 1678  df-eu 2313  df-mo 2314
This theorem is referenced by:  mo3  2346  mo  2347  rmo2  3367  nmo  28169  bj-eu3f  31486  bj-mo3OLD  31491
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