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Mirrors > Home > MPE Home > Th. List > Mathboxes > frege55lem2b | Structured version Visualization version GIF version |
Description: Lemma for frege55b 42257. 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 42254 | . 2 ⊢ [𝑥 / 𝑧]𝑧 = 𝑥 | |
2 | frege53b 42250 | . 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 2068 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1798 ax-4 1812 ax-5 1914 ax-6 1972 ax-7 2012 ax-8 2109 ax-9 2117 ax-10 2138 ax-12 2172 ax-13 2371 ax-ext 2704 ax-frege8 42169 ax-frege52c 42248 |
This theorem depends on definitions: df-bi 206 df-an 398 df-or 847 df-ex 1783 df-nf 1787 df-sb 2069 df-clab 2711 df-cleq 2725 df-clel 2811 df-sbc 3741 |
This theorem is referenced by: frege55b 42257 |
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