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Theorem unssi 3146
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_  C
unssi.2  |-  B  C_  C
Assertion
Ref Expression
unssi  |-  ( A  u.  B )  C_  C

Proof of Theorem unssi
StepHypRef Expression
1 unssi.1 . . 3  |-  A  C_  C
2 unssi.2 . . 3  |-  B  C_  C
31, 2pm3.2i 261 . 2  |-  ( A 
C_  C  /\  B  C_  C )
4 unss 3145 . 2  |-  ( ( A  C_  C  /\  B  C_  C )  <->  ( A  u.  B )  C_  C
)
53, 4mpbi 137 1  |-  ( A  u.  B )  C_  C
Colors of variables: wff set class
Syntax hints:    /\ wa 101    u. cun 2943    C_ wss 2945
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 103  ax-ia2 104  ax-ia3 105  ax-io 640  ax-5 1352  ax-7 1353  ax-gen 1354  ax-ie1 1398  ax-ie2 1399  ax-8 1411  ax-10 1412  ax-11 1413  ax-i12 1414  ax-bndl 1415  ax-4 1416  ax-17 1435  ax-i9 1439  ax-ial 1443  ax-i5r 1444  ax-ext 2038
This theorem depends on definitions:  df-bi 114  df-tru 1262  df-nf 1366  df-sb 1662  df-clab 2043  df-cleq 2049  df-clel 2052  df-nfc 2183  df-v 2576  df-un 2950  df-in 2952  df-ss 2959
This theorem is referenced by:  undifabs  3328  inundifss  3329  dmrnssfld  4623  ltrelxr  7139  nn0ssre  8243  nn0ssz  8320
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