Theorem iunconst 3978

Description: Indexed union of a constant class, i.e. where B does not depend on x. (Contributed by NM, 5-Sep-2004.) (Proof shortened by Andrew Salmon, 25-Jul-2011.)

Assertion

Ref	Expression
iunconst	⊢ (A ≠ ∅ → ∪x ∈ A B = B)

Distinct variable groups:   x,A   x,B

Proof of Theorem iunconst

Dummy variable y is distinct from all other variables.

Step	Hyp	Ref	Expression
1		r19.9rzv 3645	. . 3 ⊢ (A ≠ ∅ → (y ∈ B ↔ ∃x ∈ A y ∈ B))
2		eliun 3974	. . 3 ⊢ (y ∈ ∪x ∈ A B ↔ ∃x ∈ A y ∈ B)
3	1, 2	syl6rbbr 255	. 2 ⊢ (A ≠ ∅ → (y ∈ ∪x ∈ A B ↔ y ∈ B))
4	3	eqrdv 2351	1 ⊢ (A ≠ ∅ → ∪x ∈ A B = B)

Syntax hints:   → wi 4   = wceq 1642   ∈ wcel 1710   ≠ wne 2517  ∃wrex 2616  ∅c0 3551  ∪ciun 3970

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2479  df-ne 2519  df-ral 2620  df-rex 2621  df-v 2862  df-nin 3212  df-compl 3213  df-in 3214  df-dif 3216  df-nul 3552  df-iun 3972

This theorem is referenced by:  iununi  4051