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Mirrors > Home > MPE Home > Th. List > sbidm | Structured version Visualization version GIF version |
Description: An idempotent law for substitution. Usage of this theorem is discouraged because it depends on ax-13 2369. (Contributed by NM, 30-Jun-1994.) (Proof shortened by Andrew Salmon, 25-May-2011.) (Proof shortened by Wolf Lammen, 13-Jul-2019.) (New usage is discouraged.) |
Ref | Expression |
---|---|
sbidm | ⊢ ([𝑦 / 𝑥][𝑦 / 𝑥]𝜑 ↔ [𝑦 / 𝑥]𝜑) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | sbcom3 2503 | . 2 ⊢ ([𝑦 / 𝑥][𝑥 / 𝑥]𝜑 ↔ [𝑦 / 𝑥][𝑦 / 𝑥]𝜑) | |
2 | sbid 2245 | . . 3 ⊢ ([𝑥 / 𝑥]𝜑 ↔ 𝜑) | |
3 | 2 | sbbii 2077 | . 2 ⊢ ([𝑦 / 𝑥][𝑥 / 𝑥]𝜑 ↔ [𝑦 / 𝑥]𝜑) |
4 | 1, 3 | bitr3i 276 | 1 ⊢ ([𝑦 / 𝑥][𝑦 / 𝑥]𝜑 ↔ [𝑦 / 𝑥]𝜑) |
Colors of variables: wff setvar class |
Syntax hints: ↔ wb 205 [wsb 2065 |
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 1911 ax-6 1969 ax-7 2009 ax-10 2135 ax-12 2169 ax-13 2369 |
This theorem depends on definitions: df-bi 206 df-an 395 df-or 844 df-ex 1780 df-nf 1784 df-sb 2066 |
This theorem is referenced by: (None) |
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