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Mirrors > Home > ILE Home > Th. List > bibi2i | GIF version |
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.) |
Ref | Expression |
---|---|
bibi.a | ⊢ (𝜑 ↔ 𝜓) |
Ref | Expression |
---|---|
bibi2i | ⊢ ((𝜒 ↔ 𝜑) ↔ (𝜒 ↔ 𝜓)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | id 19 | . . 3 ⊢ ((𝜒 ↔ 𝜑) → (𝜒 ↔ 𝜑)) | |
2 | bibi.a | . . 3 ⊢ (𝜑 ↔ 𝜓) | |
3 | 1, 2 | syl6bb 195 | . 2 ⊢ ((𝜒 ↔ 𝜑) → (𝜒 ↔ 𝜓)) |
4 | id 19 | . . 3 ⊢ ((𝜒 ↔ 𝜓) → (𝜒 ↔ 𝜓)) | |
5 | 4, 2 | syl6bbr 197 | . 2 ⊢ ((𝜒 ↔ 𝜓) → (𝜒 ↔ 𝜑)) |
6 | 3, 5 | impbii 125 | 1 ⊢ ((𝜒 ↔ 𝜑) ↔ (𝜒 ↔ 𝜓)) |
Colors of variables: wff set class |
Syntax hints: ↔ wb 104 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-ia1 105 ax-ia2 106 ax-ia3 107 |
This theorem depends on definitions: df-bi 116 |
This theorem is referenced by: bibi1i 227 bibi12i 228 bibi2d 231 pm4.71r 388 sblbis 1934 sbrbif 1936 abeq2 2249 abid2f 2307 necon4biddc 2384 pm13.183 2826 disj3 3420 euabsn2 3600 a9evsep 4058 inex1 4070 zfpair2 4140 sucel 4340 bdinex1 13268 bj-zfpair2 13279 bj-d0clsepcl 13294 |
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