Theorem unss12 4082

Description: Subclass law for union of classes. (Contributed by NM, 2-Jun-2004.)

Assertion

Ref	Expression
unss12	⊢ ((𝐴 ⊆ 𝐵 ∧ 𝐶 ⊆ 𝐷) → (𝐴 ∪ 𝐶) ⊆ (𝐵 ∪ 𝐷))

Proof of Theorem unss12

Step	Hyp	Ref	Expression
1		unss1 4079	. 2 ⊢ (𝐴 ⊆ 𝐵 → (𝐴 ∪ 𝐶) ⊆ (𝐵 ∪ 𝐶))
2		unss2 4081	. 2 ⊢ (𝐶 ⊆ 𝐷 → (𝐵 ∪ 𝐶) ⊆ (𝐵 ∪ 𝐷))
3	1, 2	sylan9ss 3900	1 ⊢ ((𝐴 ⊆ 𝐵 ∧ 𝐶 ⊆ 𝐷) → (𝐴 ∪ 𝐶) ⊆ (𝐵 ∪ 𝐷))

Syntax hints:   → wi 4   ∧ wa 399   ∪ cun 3851   ⊆ wss 3853

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1803  ax-4 1817  ax-5 1918  ax-6 1976  ax-7 2018  ax-8 2114  ax-9 2122  ax-ext 2708

This theorem depends on definitions:  df-bi 210  df-an 400  df-or 848  df-tru 1546  df-ex 1788  df-sb 2073  df-clab 2715  df-cleq 2728  df-clel 2809  df-v 3400  df-un 3858  df-in 3860  df-ss 3870

This theorem is referenced by:  pwssun  5436  fun  6559  undom  8711  finsschain  8961  trclun  14542  relexpfld  14577  mulgfval  18444  mvdco  18791  dprd2da  19383  dmdprdsplit2lem  19386  lspun  19978  spanuni  29579  sshhococi  29581  mthmpps  33211  pibt2  35274  mblfinlem3  35502  dochdmj1  39090  mptrcllem  40838  clcnvlem  40848  dfrcl2  40900  relexpss1d  40931  corclrcl  40933  relexp0a  40942  corcltrcl  40965  frege131d  40990