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| Description: Corollary of Theorem 6.12(2) of [TakeutiZaring] p. 27. (Contributed by Mario Carneiro, 17-Nov-2014.) | 
| Ref | Expression | 
|---|---|
| tz6.12i | ⊢ (𝐵 ≠ ∅ → ((𝐹‘𝐴) = 𝐵 → 𝐴𝐹𝐵)) | 
| Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | fvex 6919 | . . . . 5 ⊢ (𝐹‘𝐴) ∈ V | |
| 2 | neeq1 3003 | . . . . . . . 8 ⊢ ((𝐹‘𝐴) = 𝑦 → ((𝐹‘𝐴) ≠ ∅ ↔ 𝑦 ≠ ∅)) | |
| 3 | tz6.12-2 6894 | . . . . . . . . . . 11 ⊢ (¬ ∃!𝑦 𝐴𝐹𝑦 → (𝐹‘𝐴) = ∅) | |
| 4 | 3 | necon1ai 2968 | . . . . . . . . . 10 ⊢ ((𝐹‘𝐴) ≠ ∅ → ∃!𝑦 𝐴𝐹𝑦) | 
| 5 | tz6.12c 6928 | . . . . . . . . . 10 ⊢ (∃!𝑦 𝐴𝐹𝑦 → ((𝐹‘𝐴) = 𝑦 ↔ 𝐴𝐹𝑦)) | |
| 6 | 4, 5 | syl 17 | . . . . . . . . 9 ⊢ ((𝐹‘𝐴) ≠ ∅ → ((𝐹‘𝐴) = 𝑦 ↔ 𝐴𝐹𝑦)) | 
| 7 | 6 | biimpcd 249 | . . . . . . . 8 ⊢ ((𝐹‘𝐴) = 𝑦 → ((𝐹‘𝐴) ≠ ∅ → 𝐴𝐹𝑦)) | 
| 8 | 2, 7 | sylbird 260 | . . . . . . 7 ⊢ ((𝐹‘𝐴) = 𝑦 → (𝑦 ≠ ∅ → 𝐴𝐹𝑦)) | 
| 9 | 8 | eqcoms 2745 | . . . . . 6 ⊢ (𝑦 = (𝐹‘𝐴) → (𝑦 ≠ ∅ → 𝐴𝐹𝑦)) | 
| 10 | neeq1 3003 | . . . . . 6 ⊢ (𝑦 = (𝐹‘𝐴) → (𝑦 ≠ ∅ ↔ (𝐹‘𝐴) ≠ ∅)) | |
| 11 | breq2 5147 | . . . . . 6 ⊢ (𝑦 = (𝐹‘𝐴) → (𝐴𝐹𝑦 ↔ 𝐴𝐹(𝐹‘𝐴))) | |
| 12 | 9, 10, 11 | 3imtr3d 293 | . . . . 5 ⊢ (𝑦 = (𝐹‘𝐴) → ((𝐹‘𝐴) ≠ ∅ → 𝐴𝐹(𝐹‘𝐴))) | 
| 13 | 1, 12 | vtocle 3555 | . . . 4 ⊢ ((𝐹‘𝐴) ≠ ∅ → 𝐴𝐹(𝐹‘𝐴)) | 
| 14 | 13 | a1i 11 | . . 3 ⊢ ((𝐹‘𝐴) = 𝐵 → ((𝐹‘𝐴) ≠ ∅ → 𝐴𝐹(𝐹‘𝐴))) | 
| 15 | neeq1 3003 | . . 3 ⊢ ((𝐹‘𝐴) = 𝐵 → ((𝐹‘𝐴) ≠ ∅ ↔ 𝐵 ≠ ∅)) | |
| 16 | breq2 5147 | . . 3 ⊢ ((𝐹‘𝐴) = 𝐵 → (𝐴𝐹(𝐹‘𝐴) ↔ 𝐴𝐹𝐵)) | |
| 17 | 14, 15, 16 | 3imtr3d 293 | . 2 ⊢ ((𝐹‘𝐴) = 𝐵 → (𝐵 ≠ ∅ → 𝐴𝐹𝐵)) | 
| 18 | 17 | com12 32 | 1 ⊢ (𝐵 ≠ ∅ → ((𝐹‘𝐴) = 𝐵 → 𝐴𝐹𝐵)) | 
| Colors of variables: wff setvar class | 
| Syntax hints: → wi 4 ↔ wb 206 = wceq 1540 ∃!weu 2568 ≠ wne 2940 ∅c0 4333 class class class wbr 5143 ‘cfv 6561 | 
| 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-10 2141 ax-11 2157 ax-12 2177 ax-ext 2708 ax-nul 5306 | 
| This theorem depends on definitions: df-bi 207 df-an 396 df-or 849 df-3an 1089 df-tru 1543 df-fal 1553 df-ex 1780 df-nf 1784 df-sb 2065 df-mo 2540 df-eu 2569 df-clab 2715 df-cleq 2729 df-clel 2816 df-ne 2941 df-ral 3062 df-rex 3071 df-rab 3437 df-v 3482 df-dif 3954 df-un 3956 df-ss 3968 df-nul 4334 df-if 4526 df-sn 4627 df-pr 4629 df-op 4633 df-uni 4908 df-br 5144 df-iota 6514 df-fv 6569 | 
| This theorem is referenced by: fvbr0 6935 fvclss 7261 dcomex 10487 | 
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