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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  1831  sbrbif  1833  abeq2  2143  abid2f  2199  necon4biddc  2274  pm13.183  2675  disj3  3266  euabsn2  3430  a9evsep  3870  inex1  3882  zfpair2  3936  sucel  4113  bdinex1  9330  bj-zfpair2  9341  bj-d0clsepcl  9360
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