Theorem unssi 3339

Description: An inference showing the union of two subclasses is a subclass. (Contributed by Raph Levien, 10-Dec-2002.)

Hypotheses

Ref	Expression
unssi.1	⊢ 𝐴 ⊆ 𝐶
unssi.2	⊢ 𝐵 ⊆ 𝐶

Assertion

Ref	Expression
unssi	⊢ (𝐴 ∪ 𝐵) ⊆ 𝐶

Proof of Theorem unssi

Step	Hyp	Ref	Expression
1		unssi.1	. . 3 ⊢ 𝐴 ⊆ 𝐶
2		unssi.2	. . 3 ⊢ 𝐵 ⊆ 𝐶
3	1, 2	pm3.2i 272	. 2 ⊢ (𝐴 ⊆ 𝐶 ∧ 𝐵 ⊆ 𝐶)
4		unss 3338	. 2 ⊢ ((𝐴 ⊆ 𝐶 ∧ 𝐵 ⊆ 𝐶) ↔ (𝐴 ∪ 𝐵) ⊆ 𝐶)
5	3, 4	mpbi 145	1 ⊢ (𝐴 ∪ 𝐵) ⊆ 𝐶

Syntax hints:   ∧ wa 104   ∪ cun 3155   ⊆ wss 3157

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 710  ax-5 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-10 1519  ax-11 1520  ax-i12 1521  ax-bndl 1523  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548  ax-i5r 1549  ax-ext 2178

This theorem depends on definitions:  df-bi 117  df-tru 1367  df-nf 1475  df-sb 1777  df-clab 2183  df-cleq 2189  df-clel 2192  df-nfc 2328  df-v 2765  df-un 3161  df-in 3163  df-ss 3170

This theorem is referenced by:  undifabs  3528  inundifss  3529  dmrnssfld  4930  caserel  7162  ltrelxr  8104  nn0ssre  9270  nn0ssz  9361  strleun  12807