Theorem un00 4343

Description: Two classes are empty iff their union is empty. (Contributed by NM, 11-Aug-2004.)

Assertion

Ref	Expression
un00	⊢ ((𝐴 = ∅ ∧ 𝐵 = ∅) ↔ (𝐴 ∪ 𝐵) = ∅)

Proof of Theorem un00

Step	Hyp	Ref	Expression
1		uneq12 4066	. . 3 ⊢ ((𝐴 = ∅ ∧ 𝐵 = ∅) → (𝐴 ∪ 𝐵) = (∅ ∪ ∅))
2		un0 4290	. . 3 ⊢ (∅ ∪ ∅) = ∅
3	1, 2	eqtrdi 2810	. 2 ⊢ ((𝐴 = ∅ ∧ 𝐵 = ∅) → (𝐴 ∪ 𝐵) = ∅)
4		ssun1 4080	. . . . 5 ⊢ 𝐴 ⊆ (𝐴 ∪ 𝐵)
5		sseq2 3921	. . . . 5 ⊢ ((𝐴 ∪ 𝐵) = ∅ → (𝐴 ⊆ (𝐴 ∪ 𝐵) ↔ 𝐴 ⊆ ∅))
6	4, 5	mpbii 236	. . . 4 ⊢ ((𝐴 ∪ 𝐵) = ∅ → 𝐴 ⊆ ∅)
7		ss0b 4297	. . . 4 ⊢ (𝐴 ⊆ ∅ ↔ 𝐴 = ∅)
8	6, 7	sylib 221	. . 3 ⊢ ((𝐴 ∪ 𝐵) = ∅ → 𝐴 = ∅)
9		ssun2 4081	. . . . 5 ⊢ 𝐵 ⊆ (𝐴 ∪ 𝐵)
10		sseq2 3921	. . . . 5 ⊢ ((𝐴 ∪ 𝐵) = ∅ → (𝐵 ⊆ (𝐴 ∪ 𝐵) ↔ 𝐵 ⊆ ∅))
11	9, 10	mpbii 236	. . . 4 ⊢ ((𝐴 ∪ 𝐵) = ∅ → 𝐵 ⊆ ∅)
12		ss0b 4297	. . . 4 ⊢ (𝐵 ⊆ ∅ ↔ 𝐵 = ∅)
13	11, 12	sylib 221	. . 3 ⊢ ((𝐴 ∪ 𝐵) = ∅ → 𝐵 = ∅)
14	8, 13	jca 515	. 2 ⊢ ((𝐴 ∪ 𝐵) = ∅ → (𝐴 = ∅ ∧ 𝐵 = ∅))
15	3, 14	impbii 212	1 ⊢ ((𝐴 = ∅ ∧ 𝐵 = ∅) ↔ (𝐴 ∪ 𝐵) = ∅)

Syntax hints:   ↔ wb 209   ∧ wa 399   = wceq 1539   ∪ cun 3859   ⊆ wss 3861  ∅c0 4228

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1798  ax-4 1812  ax-5 1912  ax-6 1971  ax-7 2016  ax-8 2114  ax-9 2122  ax-ext 2730

This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-tru 1542  df-ex 1783  df-sb 2071  df-clab 2737  df-cleq 2751  df-clel 2831  df-v 3412  df-dif 3864  df-un 3866  df-in 3868  df-ss 3878  df-nul 4229

This theorem is referenced by:  undisj1  4362  undisj2  4363  disjpr2  4610  rankxplim3  9357  ssxr  10762  rpnnen2lem12  15640  wwlksnext  27793  asindmre  35456  iunrelexp0  40822  uneqsn  41145