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Theorem alimex 1652
 Description: A utility theorem. An interesting case is when the same formula is substituted for both and , since then both implications express a type of non-freeness. See also eximal 1615. (Contributed by BJ, 12-May-2019.)
Assertion
Ref Expression
alimex

Proof of Theorem alimex
StepHypRef Expression
1 alex 1647 . . 3
21imbi2i 312 . 2
3 con2b 334 . 2
42, 3bitri 249 1
 Colors of variables: wff setvar class Syntax hints:  -.wn 3  ->wi 4  <->wb 184  A.wal 1393  E.wex 1612 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1618  ax-4 1631 This theorem depends on definitions:  df-bi 185  df-ex 1613
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