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Syntax Definition ciun 3921
Description: Extend class notation to include indexed union. Note: Historically (prior to 21-Oct-2005), set.mm used the notation  U. x  e.  A B, with the same union symbol as cuni 3843. While that syntax was unambiguous, it did not allow for LALR parsing of the syntax constructions in set.mm. The new syntax uses as distinguished symbol  U_ instead of  U. and does allow LALR parsing. Thanks to Peter Backes for suggesting this change.
Hypotheses
Ref Expression
vx  set  x
cA  class  A
cB  class  B
Assertion
Ref Expression
ciun  class  U_ x  e.  A  B

See definition df-iun 3923 for more information.

Colors of variables: wff set class
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