Theorem dfmoeu 2529

Description: An elementary proof of moeu 2576 in disguise, connecting an expression characterizing uniqueness (df-mo 2533) to that of existential uniqueness (eu6 2567). No particular order of definition is required, as one can be derived from the other. This is shown here and in dfeumo 2530. (Contributed by Wolf Lammen, 27-May-2019.)

Assertion

Ref	Expression
dfmoeu	⊢ ((∃𝑥𝜑 → ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) ↔ ∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦))

Distinct variable groups:   𝑥,𝑦   𝜑,𝑦

Allowed substitution hint:   𝜑(𝑥)

Proof of Theorem dfmoeu

Step	Hyp	Ref	Expression
1		alnex 1782	. . . . 5 ⊢ (∀𝑥 ¬ 𝜑 ↔ ¬ ∃𝑥𝜑)
2		pm2.21 123	. . . . . 6 ⊢ (¬ 𝜑 → (𝜑 → 𝑥 = 𝑦))
3	2	alimi 1812	. . . . 5 ⊢ (∀𝑥 ¬ 𝜑 → ∀𝑥(𝜑 → 𝑥 = 𝑦))
4	1, 3	sylbir 234	. . . 4 ⊢ (¬ ∃𝑥𝜑 → ∀𝑥(𝜑 → 𝑥 = 𝑦))
5	4	19.8ad 2174	. . 3 ⊢ (¬ ∃𝑥𝜑 → ∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦))
6		biimp 214	. . . . 5 ⊢ ((𝜑 ↔ 𝑥 = 𝑦) → (𝜑 → 𝑥 = 𝑦))
7	6	alimi 1812	. . . 4 ⊢ (∀𝑥(𝜑 ↔ 𝑥 = 𝑦) → ∀𝑥(𝜑 → 𝑥 = 𝑦))
8	7	eximi 1836	. . 3 ⊢ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) → ∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦))
9	5, 8	ja 186	. 2 ⊢ ((∃𝑥𝜑 → ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) → ∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦))
10		nfia1 2149	. . . . 5 ⊢ Ⅎ𝑥(∀𝑥(𝜑 → 𝑥 = 𝑦) → ∀𝑥(𝜑 ↔ 𝑥 = 𝑦))
11		id 22	. . . . . . . . 9 ⊢ (𝜑 → 𝜑)
12		ax12v 2171	. . . . . . . . . 10 ⊢ (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑)))
13	12	com12 32	. . . . . . . . 9 ⊢ (𝜑 → (𝑥 = 𝑦 → ∀𝑥(𝑥 = 𝑦 → 𝜑)))
14	11, 13	embantd 59	. . . . . . . 8 ⊢ (𝜑 → ((𝜑 → 𝑥 = 𝑦) → ∀𝑥(𝑥 = 𝑦 → 𝜑)))
15	14	spsd 2179	. . . . . . 7 ⊢ (𝜑 → (∀𝑥(𝜑 → 𝑥 = 𝑦) → ∀𝑥(𝑥 = 𝑦 → 𝜑)))
16	15	ancld 550	. . . . . 6 ⊢ (𝜑 → (∀𝑥(𝜑 → 𝑥 = 𝑦) → (∀𝑥(𝜑 → 𝑥 = 𝑦) ∧ ∀𝑥(𝑥 = 𝑦 → 𝜑))))
17		albiim 1891	. . . . . 6 ⊢ (∀𝑥(𝜑 ↔ 𝑥 = 𝑦) ↔ (∀𝑥(𝜑 → 𝑥 = 𝑦) ∧ ∀𝑥(𝑥 = 𝑦 → 𝜑)))
18	16, 17	imbitrrdi 251	. . . . 5 ⊢ (𝜑 → (∀𝑥(𝜑 → 𝑥 = 𝑦) → ∀𝑥(𝜑 ↔ 𝑥 = 𝑦)))
19	10, 18	exlimi 2209	. . . 4 ⊢ (∃𝑥𝜑 → (∀𝑥(𝜑 → 𝑥 = 𝑦) → ∀𝑥(𝜑 ↔ 𝑥 = 𝑦)))
20	19	eximdv 1919	. . 3 ⊢ (∃𝑥𝜑 → (∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦) → ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)))
21	20	com12 32	. 2 ⊢ (∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦) → (∃𝑥𝜑 → ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)))
22	9, 21	impbii 208	1 ⊢ ((∃𝑥𝜑 → ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) ↔ ∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦))

Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 205   ∧ wa 395  ∀wal 1538  ∃wex 1780

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1796  ax-4 1810  ax-5 1912  ax-6 1970  ax-7 2010  ax-10 2136  ax-12 2170

This theorem depends on definitions:  df-bi 206  df-an 396  df-or 845  df-ex 1781  df-nf 1785

This theorem is referenced by:  dfeumo  2530  eu6  2567  dfmo  2589