Theorem disjnf 32659

Description: In case 𝑥 is not free in 𝐵, disjointness is not so interesting since it reduces to cases where 𝐴 is a singleton. (Google Groups discussion with Peter Mazsa.) (Contributed by Thierry Arnoux, 26-Jul-2018.)

Assertion

Ref	Expression
disjnf	⊢ (Disj 𝑥 ∈ 𝐴 𝐵 ↔ (𝐵 = ∅ ∨ ∃*𝑥 𝑥 ∈ 𝐴))

Distinct variable groups:   𝑥,𝐴   𝑥,𝐵

Proof of Theorem disjnf

Dummy variable 𝑦 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		inidm 4155	. . . 4 ⊢ (𝐵 ∩ 𝐵) = 𝐵
2	1	eqeq1i 2744	. . 3 ⊢ ((𝐵 ∩ 𝐵) = ∅ ↔ 𝐵 = ∅)
3	2	orbi1i 919	. 2 ⊢ (((𝐵 ∩ 𝐵) = ∅ ∨ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 𝑥 = 𝑦) ↔ (𝐵 = ∅ ∨ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 𝑥 = 𝑦))
4		eqidd 2740	. . . 4 ⊢ (𝑥 = 𝑦 → 𝐵 = 𝐵)
5	4	disjor 5054	. . 3 ⊢ (Disj 𝑥 ∈ 𝐴 𝐵 ↔ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 (𝑥 = 𝑦 ∨ (𝐵 ∩ 𝐵) = ∅))
6		orcom 876	. . . . . 6 ⊢ ((𝑥 = 𝑦 ∨ (𝐵 ∩ 𝐵) = ∅) ↔ ((𝐵 ∩ 𝐵) = ∅ ∨ 𝑥 = 𝑦))
7	6	ralbii 3085	. . . . 5 ⊢ (∀𝑦 ∈ 𝐴 (𝑥 = 𝑦 ∨ (𝐵 ∩ 𝐵) = ∅) ↔ ∀𝑦 ∈ 𝐴 ((𝐵 ∩ 𝐵) = ∅ ∨ 𝑥 = 𝑦))
8		r19.32v 3172	. . . . 5 ⊢ (∀𝑦 ∈ 𝐴 ((𝐵 ∩ 𝐵) = ∅ ∨ 𝑥 = 𝑦) ↔ ((𝐵 ∩ 𝐵) = ∅ ∨ ∀𝑦 ∈ 𝐴 𝑥 = 𝑦))
9	7, 8	bitri 276	. . . 4 ⊢ (∀𝑦 ∈ 𝐴 (𝑥 = 𝑦 ∨ (𝐵 ∩ 𝐵) = ∅) ↔ ((𝐵 ∩ 𝐵) = ∅ ∨ ∀𝑦 ∈ 𝐴 𝑥 = 𝑦))
10	9	ralbii 3085	. . 3 ⊢ (∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 (𝑥 = 𝑦 ∨ (𝐵 ∩ 𝐵) = ∅) ↔ ∀𝑥 ∈ 𝐴 ((𝐵 ∩ 𝐵) = ∅ ∨ ∀𝑦 ∈ 𝐴 𝑥 = 𝑦))
11		r19.32v 3172	. . 3 ⊢ (∀𝑥 ∈ 𝐴 ((𝐵 ∩ 𝐵) = ∅ ∨ ∀𝑦 ∈ 𝐴 𝑥 = 𝑦) ↔ ((𝐵 ∩ 𝐵) = ∅ ∨ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 𝑥 = 𝑦))
12	5, 10, 11	3bitri 298	. 2 ⊢ (Disj 𝑥 ∈ 𝐴 𝐵 ↔ ((𝐵 ∩ 𝐵) = ∅ ∨ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 𝑥 = 𝑦))
13		moel 3364	. . 3 ⊢ (∃*𝑥 𝑥 ∈ 𝐴 ↔ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 𝑥 = 𝑦)
14	13	orbi2i 918	. 2 ⊢ ((𝐵 = ∅ ∨ ∃*𝑥 𝑥 ∈ 𝐴) ↔ (𝐵 = ∅ ∨ ∀𝑥 ∈ 𝐴 ∀𝑦 ∈ 𝐴 𝑥 = 𝑦))
15	3, 12, 14	3bitr4i 304	1 ⊢ (Disj 𝑥 ∈ 𝐴 𝐵 ↔ (𝐵 = ∅ ∨ ∃*𝑥 𝑥 ∈ 𝐴))

Syntax hints:   ↔ wb 207   ∨ wo 853   = wceq 1547   ∈ wcel 2119  ∃*wmo 2541  ∀wral 3053   ∩ cin 3882  ∅c0 4261  Disj wdisj 5039

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1802  ax-4 1816  ax-5 1917  ax-6 1974  ax-7 2015  ax-8 2121  ax-9 2129  ax-11 2168  ax-ext 2711

This theorem depends on definitions:  df-bi 208  df-an 397  df-or 854  df-tru 1550  df-fal 1560  df-ex 1787  df-sb 2074  df-mo 2543  df-clab 2718  df-cleq 2731  df-clel 2814  df-ral 3054  df-rmo 3344  df-v 3433  df-dif 3886  df-in 3890  df-nul 4262  df-disj 5040

This theorem is referenced by: (None)