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Mirrors > Home > ILE Home > Th. List > dfbi2 | GIF version |
Description: A theorem similar to the standard definition of the biconditional. Definition of [Margaris] p. 49. (Contributed by NM, 5-Aug-1993.) (Revised by NM, 31-Jan-2015.) |
Ref | Expression |
---|---|
dfbi2 | ⊢ ((𝜑 ↔ 𝜓) ↔ ((𝜑 → 𝜓) ∧ (𝜓 → 𝜑))) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-bi 116 | . . 3 ⊢ (((𝜑 ↔ 𝜓) → ((𝜑 → 𝜓) ∧ (𝜓 → 𝜑))) ∧ (((𝜑 → 𝜓) ∧ (𝜓 → 𝜑)) → (𝜑 ↔ 𝜓))) | |
2 | 1 | simpli 110 | . 2 ⊢ ((𝜑 ↔ 𝜓) → ((𝜑 → 𝜓) ∧ (𝜓 → 𝜑))) |
3 | 1 | simpri 112 | . 2 ⊢ (((𝜑 → 𝜓) ∧ (𝜓 → 𝜑)) → (𝜑 ↔ 𝜓)) |
4 | 2, 3 | impbii 125 | 1 ⊢ ((𝜑 ↔ 𝜓) ↔ ((𝜑 → 𝜓) ∧ (𝜓 → 𝜑))) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∧ wa 103 ↔ wb 104 |
This theorem was proved from axioms: ax-1 5 ax-2 6 ax-mp 7 ax-ia1 105 ax-ia2 106 ax-ia3 107 |
This theorem depends on definitions: df-bi 116 |
This theorem is referenced by: pm4.71 382 pm5.17dc 849 dcbi 883 orbididc 900 trubifal 1353 albiim 1422 hbbi 1486 hbbid 1513 nfbid 1526 spsbbi 1773 sbbi 1882 cleqh 2188 ralbiim 2504 reu8 2812 sseq2 3049 soeq2 4152 fun11 5094 dffo3 5460 bdbi 11990 |
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