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Mirrors > Home > MPE Home > Th. List > sb1 | Structured version Visualization version GIF version |
Description: One direction of a simplified definition of substitution. The converse requires either a disjoint variable condition (sb5 2272) or a non-freeness hypothesis (sb5f 2534). Usage of this theorem is discouraged because it depends on ax-13 2386. Use the weaker sb1v 2091 when possible. (Contributed by NM, 13-May-1993.) Revise df-sb 2066. (Revised by Wolf Lammen, 21-Feb-2024.) (New usage is discouraged.) |
Ref | Expression |
---|---|
sb1 | ⊢ ([𝑦 / 𝑥]𝜑 → ∃𝑥(𝑥 = 𝑦 ∧ 𝜑)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | spsbe 2084 | . . 3 ⊢ ([𝑦 / 𝑥]𝜑 → ∃𝑥𝜑) | |
2 | pm3.2 472 | . . . 4 ⊢ (𝑥 = 𝑦 → (𝜑 → (𝑥 = 𝑦 ∧ 𝜑))) | |
3 | 2 | aleximi 1828 | . . 3 ⊢ (∀𝑥 𝑥 = 𝑦 → (∃𝑥𝜑 → ∃𝑥(𝑥 = 𝑦 ∧ 𝜑))) |
4 | 1, 3 | syl5 34 | . 2 ⊢ (∀𝑥 𝑥 = 𝑦 → ([𝑦 / 𝑥]𝜑 → ∃𝑥(𝑥 = 𝑦 ∧ 𝜑))) |
5 | sb3b 2497 | . . 3 ⊢ (¬ ∀𝑥 𝑥 = 𝑦 → ([𝑦 / 𝑥]𝜑 ↔ ∃𝑥(𝑥 = 𝑦 ∧ 𝜑))) | |
6 | 5 | biimpd 231 | . 2 ⊢ (¬ ∀𝑥 𝑥 = 𝑦 → ([𝑦 / 𝑥]𝜑 → ∃𝑥(𝑥 = 𝑦 ∧ 𝜑))) |
7 | 4, 6 | pm2.61i 184 | 1 ⊢ ([𝑦 / 𝑥]𝜑 → ∃𝑥(𝑥 = 𝑦 ∧ 𝜑)) |
Colors of variables: wff setvar class |
Syntax hints: ¬ wn 3 → wi 4 ∧ wa 398 ∀wal 1531 ∃wex 1776 [wsb 2065 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1792 ax-4 1806 ax-5 1907 ax-6 1966 ax-7 2011 ax-10 2141 ax-12 2173 ax-13 2386 |
This theorem depends on definitions: df-bi 209 df-an 399 df-or 844 df-ex 1777 df-nf 1781 df-sb 2066 |
This theorem is referenced by: sb3bOLD 2504 dfsb1 2506 spsbeOLDOLD 2507 sb4vOLDOLD 2509 sb4e 2520 |
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