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Theorem bibi2i 216
Description: Inference adding a biconditional to the left in an equivalence. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 7-May-2011.) (Proof shortened by Wolf Lammen, 16-May-2013.)
Hypothesis
Ref Expression
bibi.a (φψ)
Assertion
Ref Expression
bibi2i ((χφ) ↔ (χψ))

Proof of Theorem bibi2i
StepHypRef Expression
1 id 19 . . 3 ((χφ) → (χφ))
2 bibi.a . . 3 (φψ)
31, 2syl6bb 185 . 2 ((χφ) → (χψ))
4 id 19 . . 3 ((χψ) → (χψ))
54, 2syl6bbr 187 . 2 ((χψ) → (χφ))
63, 5impbii 117 1 ((χφ) ↔ (χψ))
Colors of variables: wff set class
Syntax hints:  wb 98
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101
This theorem depends on definitions:  df-bi 110
This theorem is referenced by:  bibi1i  217  bibi12i  218  bibi2d  221  pm4.71r  370  sblbis  1812  sbrbif  1814  abeq2  2124  abid2f  2180  necon4biddc  2254  pm13.183  2654  disj3  3245  euabsn2  3409  a9evsep  3849  inex1  3861  zfpair2  3915  sucel  4092  bdinex1  7261  bj-zfpair2  7272  bj-d0clsepcl  7287
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