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Theorem unopnOLD 25832
Description: The union of two open sets is open. (Moved to unopn 16612 in main set.mm and may be deleted by mathbox owner, JM. --NM 15-Oct-2012.) (Contributed by Jeff Madsen, 2-Sep-2009.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
unopnOLD  |-  ( ( J  e.  Top  /\  A  e.  J  /\  B  e.  J )  ->  ( A  u.  B
)  e.  J )

Proof of Theorem unopnOLD
StepHypRef Expression
1 unopn 16612 1  |-  ( ( J  e.  Top  /\  A  e.  J  /\  B  e.  J )  ->  ( A  u.  B
)  e.  J )
Colors of variables: wff set class
Syntax hints:    -> wi 6    /\ w3a 939    e. wcel 1621    u. cun 3125   Topctop 16594
This theorem was proved from axioms:  ax-1 7  ax-2 8  ax-3 9  ax-mp 10  ax-5 1533  ax-6 1534  ax-7 1535  ax-gen 1536  ax-8 1623  ax-11 1624  ax-17 1628  ax-12o 1664  ax-10 1678  ax-9 1684  ax-4 1692  ax-16 1927  ax-ext 2239  ax-sep 4115
This theorem depends on definitions:  df-bi 179  df-or 361  df-an 362  df-3an 941  df-tru 1315  df-ex 1538  df-nf 1540  df-sb 1884  df-clab 2245  df-cleq 2251  df-clel 2254  df-nfc 2383  df-ral 2523  df-rex 2524  df-v 2765  df-un 3132  df-in 3134  df-ss 3141  df-pw 3601  df-sn 3620  df-pr 3621  df-uni 3802  df-top 16599
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