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Mirrors > Home > MPE Home > Th. List > Mathboxes > frege55lem2b | Structured version Visualization version GIF version |
Description: Lemma for frege55b 40250. Core proof of Proposition 55 of [Frege1879] p. 50. (Contributed by RP, 24-Dec-2019.) (Proof modification is discouraged.) |
Ref | Expression |
---|---|
frege55lem2b | ⊢ (𝑥 = 𝑦 → [𝑦 / 𝑧]𝑧 = 𝑥) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | frege54cor1b 40247 | . 2 ⊢ [𝑥 / 𝑧]𝑧 = 𝑥 | |
2 | frege53b 40243 | . 2 ⊢ ([𝑥 / 𝑧]𝑧 = 𝑥 → (𝑥 = 𝑦 → [𝑦 / 𝑧]𝑧 = 𝑥)) | |
3 | 1, 2 | ax-mp 5 | 1 ⊢ (𝑥 = 𝑦 → [𝑦 / 𝑧]𝑧 = 𝑥) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 [wsb 2069 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1796 ax-4 1810 ax-5 1911 ax-6 1970 ax-7 2015 ax-8 2116 ax-9 2124 ax-10 2145 ax-12 2177 ax-13 2390 ax-ext 2795 ax-frege8 40162 ax-frege52c 40241 |
This theorem depends on definitions: df-bi 209 df-an 399 df-or 844 df-ex 1781 df-nf 1785 df-sb 2070 df-clab 2802 df-cleq 2816 df-clel 2895 df-sbc 3775 |
This theorem is referenced by: frege55b 40250 |
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