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Theorem mo3 2495
 Description: Alternate definition of "at most one." Definition of [BellMachover] p. 460, except that definition has the side condition that 𝑦 not occur in 𝜑 in place of our hypothesis. (Contributed by NM, 8-Mar-1995.) (Proof shortened by Wolf Lammen, 18-Aug-2019.)
Hypothesis
Ref Expression
mo3.1 𝑦𝜑
Assertion
Ref Expression
mo3 (∃*𝑥𝜑 ↔ ∀𝑥𝑦((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦))
Distinct variable group:   𝑥,𝑦
Allowed substitution hints:   𝜑(𝑥,𝑦)

Proof of Theorem mo3
Dummy variable 𝑧 is distinct from all other variables.
StepHypRef Expression
1 nfmo1 2469 . . 3 𝑥∃*𝑥𝜑
2 mo3.1 . . . . 5 𝑦𝜑
32nfmo 2475 . . . 4 𝑦∃*𝑥𝜑
4 mo2v 2465 . . . . 5 (∃*𝑥𝜑 ↔ ∃𝑧𝑥(𝜑𝑥 = 𝑧))
5 sp 2041 . . . . . . . 8 (∀𝑥(𝜑𝑥 = 𝑧) → (𝜑𝑥 = 𝑧))
6 spsbim 2382 . . . . . . . . 9 (∀𝑥(𝜑𝑥 = 𝑧) → ([𝑦 / 𝑥]𝜑 → [𝑦 / 𝑥]𝑥 = 𝑧))
7 equsb3 2420 . . . . . . . . 9 ([𝑦 / 𝑥]𝑥 = 𝑧𝑦 = 𝑧)
86, 7syl6ib 240 . . . . . . . 8 (∀𝑥(𝜑𝑥 = 𝑧) → ([𝑦 / 𝑥]𝜑𝑦 = 𝑧))
95, 8anim12d 584 . . . . . . 7 (∀𝑥(𝜑𝑥 = 𝑧) → ((𝜑 ∧ [𝑦 / 𝑥]𝜑) → (𝑥 = 𝑧𝑦 = 𝑧)))
10 equtr2 1941 . . . . . . 7 ((𝑥 = 𝑧𝑦 = 𝑧) → 𝑥 = 𝑦)
119, 10syl6 34 . . . . . 6 (∀𝑥(𝜑𝑥 = 𝑧) → ((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦))
1211exlimiv 1845 . . . . 5 (∃𝑧𝑥(𝜑𝑥 = 𝑧) → ((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦))
134, 12sylbi 206 . . . 4 (∃*𝑥𝜑 → ((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦))
143, 13alrimi 2069 . . 3 (∃*𝑥𝜑 → ∀𝑦((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦))
151, 14alrimi 2069 . 2 (∃*𝑥𝜑 → ∀𝑥𝑦((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦))
16 nfs1v 2425 . . . . . . . 8 𝑥[𝑦 / 𝑥]𝜑
17 pm3.21 463 . . . . . . . . 9 ([𝑦 / 𝑥]𝜑 → (𝜑 → (𝜑 ∧ [𝑦 / 𝑥]𝜑)))
1817imim1d 80 . . . . . . . 8 ([𝑦 / 𝑥]𝜑 → (((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦) → (𝜑𝑥 = 𝑦)))
1916, 18alimd 2068 . . . . . . 7 ([𝑦 / 𝑥]𝜑 → (∀𝑥((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦) → ∀𝑥(𝜑𝑥 = 𝑦)))
2019com12 32 . . . . . 6 (∀𝑥((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦) → ([𝑦 / 𝑥]𝜑 → ∀𝑥(𝜑𝑥 = 𝑦)))
2120aleximi 1749 . . . . 5 (∀𝑦𝑥((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦) → (∃𝑦[𝑦 / 𝑥]𝜑 → ∃𝑦𝑥(𝜑𝑥 = 𝑦)))
222sb8e 2413 . . . . 5 (∃𝑥𝜑 ↔ ∃𝑦[𝑦 / 𝑥]𝜑)
232mo2 2467 . . . . 5 (∃*𝑥𝜑 ↔ ∃𝑦𝑥(𝜑𝑥 = 𝑦))
2421, 22, 233imtr4g 284 . . . 4 (∀𝑦𝑥((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦) → (∃𝑥𝜑 → ∃*𝑥𝜑))
25 moabs 2489 . . . 4 (∃*𝑥𝜑 ↔ (∃𝑥𝜑 → ∃*𝑥𝜑))
2624, 25sylibr 223 . . 3 (∀𝑦𝑥((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦) → ∃*𝑥𝜑)
2726alcoms 2022 . 2 (∀𝑥𝑦((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦) → ∃*𝑥𝜑)
2815, 27impbii 198 1 (∃*𝑥𝜑 ↔ ∀𝑥𝑦((𝜑 ∧ [𝑦 / 𝑥]𝜑) → 𝑥 = 𝑦))
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ↔ wb 195   ∧ wa 383  ∀wal 1473  ∃wex 1695  Ⅎwnf 1699  [wsb 1867  ∃*wmo 2459 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1713  ax-4 1728  ax-5 1827  ax-6 1875  ax-7 1922  ax-10 2006  ax-11 2021  ax-12 2034  ax-13 2234 This theorem depends on definitions:  df-bi 196  df-or 384  df-an 385  df-tru 1478  df-ex 1696  df-nf 1701  df-sb 1868  df-eu 2462  df-mo 2463 This theorem is referenced by:  mo  2496  eu2  2497  mo4f  2504  2mo  2539  rmo3  3494  isarep2  5892  mo5f  28708  rmo3f  28719  rmo4fOLD  28720  bnj580  30237  pm14.12  37644
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