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Theorem e2ebind 28724
Description: Absorption of an existential quantifier of a double existential quantifier of non-distinct variables. e2ebind 28724 is derived from e2ebindVD 29098. (Contributed by Alan Sare, 27-Nov-2014.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
e2ebind  |-  ( A. x  x  =  y  ->  ( E. x E. y ph  <->  E. y ph )
)

Proof of Theorem e2ebind
StepHypRef Expression
1 nfe1 1748 . . . 4  |-  F/ y E. y ph
2119.9 1798 . . 3  |-  ( E. y E. y ph  <->  E. y ph )
3 biidd 230 . . . . . 6  |-  ( A. y  y  =  x  ->  ( ph  <->  ph ) )
43drex1 2060 . . . . 5  |-  ( A. y  y  =  x  ->  ( E. y ph  <->  E. x ph ) )
54drex2 2061 . . . 4  |-  ( A. y  y  =  x  ->  ( E. y E. y ph  <->  E. y E. x ph ) )
6 excom 1757 . . . 4  |-  ( E. y E. x ph  <->  E. x E. y ph )
75, 6syl6bb 254 . . 3  |-  ( A. y  y  =  x  ->  ( E. y E. y ph  <->  E. x E. y ph ) )
82, 7syl5rbbr 253 . 2  |-  ( A. y  y  =  x  ->  ( E. x E. y ph  <->  E. y ph )
)
98aecoms 2037 1  |-  ( A. x  x  =  y  ->  ( E. x E. y ph  <->  E. y ph )
)
Colors of variables: wff set class
Syntax hints:    -> wi 4    <-> wb 178   A.wal 1550   E.wex 1551    = wceq 1653
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1556  ax-5 1567  ax-17 1627  ax-9 1667  ax-8 1688  ax-6 1745  ax-7 1750  ax-11 1762  ax-12 1951
This theorem depends on definitions:  df-bi 179  df-an 362  df-ex 1552  df-nf 1555
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