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Theorem mopick 2564
 Description: "At most one" picks a variable value, eliminating an existential quantifier. (Contributed by NM, 27-Jan-1997.) (Proof shortened by Wolf Lammen, 17-Sep-2019.)
Assertion
Ref Expression
mopick ((∃*𝑥𝜑 ∧ ∃𝑥(𝜑𝜓)) → (𝜑𝜓))

Proof of Theorem mopick
Dummy variable 𝑦 is distinct from all other variables.
StepHypRef Expression
1 mo2v 2505 . . 3 (∃*𝑥𝜑 ↔ ∃𝑦𝑥(𝜑𝑥 = 𝑦))
2 sp 2091 . . . . 5 (∀𝑥(𝜑𝑥 = 𝑦) → (𝜑𝑥 = 𝑦))
3 pm3.45 897 . . . . . . 7 ((𝜑𝑥 = 𝑦) → ((𝜑𝜓) → (𝑥 = 𝑦𝜓)))
43aleximi 1799 . . . . . 6 (∀𝑥(𝜑𝑥 = 𝑦) → (∃𝑥(𝜑𝜓) → ∃𝑥(𝑥 = 𝑦𝜓)))
5 sb56 2188 . . . . . . 7 (∃𝑥(𝑥 = 𝑦𝜓) ↔ ∀𝑥(𝑥 = 𝑦𝜓))
6 sp 2091 . . . . . . 7 (∀𝑥(𝑥 = 𝑦𝜓) → (𝑥 = 𝑦𝜓))
75, 6sylbi 207 . . . . . 6 (∃𝑥(𝑥 = 𝑦𝜓) → (𝑥 = 𝑦𝜓))
84, 7syl6 35 . . . . 5 (∀𝑥(𝜑𝑥 = 𝑦) → (∃𝑥(𝜑𝜓) → (𝑥 = 𝑦𝜓)))
92, 8syl5d 73 . . . 4 (∀𝑥(𝜑𝑥 = 𝑦) → (∃𝑥(𝜑𝜓) → (𝜑𝜓)))
109exlimiv 1898 . . 3 (∃𝑦𝑥(𝜑𝑥 = 𝑦) → (∃𝑥(𝜑𝜓) → (𝜑𝜓)))
111, 10sylbi 207 . 2 (∃*𝑥𝜑 → (∃𝑥(𝜑𝜓) → (𝜑𝜓)))
1211imp 444 1 ((∃*𝑥𝜑 ∧ ∃𝑥(𝜑𝜓)) → (𝜑𝜓))
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ∧ wa 383  ∀wal 1521  ∃wex 1744  ∃*wmo 2499 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1762  ax-4 1777  ax-5 1879  ax-6 1945  ax-7 1981  ax-10 2059  ax-12 2087 This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-ex 1745  df-nf 1750  df-eu 2502  df-mo 2503 This theorem is referenced by:  eupick  2565  mopick2  2569  moexex  2570  morex  3423  imadif  6011  cmetss  23159
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