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Mirrors > Home > MPE Home > Th. List > Mathboxes > frege55lem2b | Structured version Visualization version GIF version |
Description: Lemma for frege55b 39030. 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 39027 | . 2 ⊢ [𝑥 / 𝑧]𝑧 = 𝑥 | |
2 | frege53b 39023 | . 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 2067 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1894 ax-4 1908 ax-5 2009 ax-6 2075 ax-7 2112 ax-9 2173 ax-12 2220 ax-13 2389 ax-ext 2803 ax-frege8 38942 ax-frege52c 39021 |
This theorem depends on definitions: df-bi 199 df-an 387 df-ex 1879 df-sb 2068 df-clab 2812 df-cleq 2818 df-clel 2821 df-sbc 3663 |
This theorem is referenced by: frege55b 39030 |
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