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| Mirrors > Home > MPE Home > Th. List > Mathboxes > ifnmfalse | Structured version Visualization version GIF version | ||
| Description: If A is not a member of B, but an "if" condition requires it, then the "false" branch results. This is a simple utility to provide a slight shortening and simplification of proofs versus applying iffalse 4534 directly in this case. (Contributed by David A. Wheeler, 15-May-2015.) | 
| Ref | Expression | 
|---|---|
| ifnmfalse | ⊢ (𝐴 ∉ 𝐵 → if(𝐴 ∈ 𝐵, 𝐶, 𝐷) = 𝐷) | 
| Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | df-nel 3047 | . 2 ⊢ (𝐴 ∉ 𝐵 ↔ ¬ 𝐴 ∈ 𝐵) | |
| 2 | iffalse 4534 | . 2 ⊢ (¬ 𝐴 ∈ 𝐵 → if(𝐴 ∈ 𝐵, 𝐶, 𝐷) = 𝐷) | |
| 3 | 1, 2 | sylbi 217 | 1 ⊢ (𝐴 ∉ 𝐵 → if(𝐴 ∈ 𝐵, 𝐶, 𝐷) = 𝐷) | 
| Colors of variables: wff setvar class | 
| Syntax hints: ¬ wn 3 → wi 4 = wceq 1540 ∈ wcel 2108 ∉ wnel 3046 ifcif 4525 | 
| This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1795 ax-4 1809 ax-5 1910 ax-6 1967 ax-7 2007 ax-8 2110 ax-9 2118 ax-ext 2708 | 
| This theorem depends on definitions: df-bi 207 df-an 396 df-or 849 df-ex 1780 df-sb 2065 df-clab 2715 df-cleq 2729 df-clel 2816 df-nel 3047 df-if 4526 | 
| This theorem is referenced by: (None) | 
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