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Syntax Definition ciun 4051
Description: Extend class notation to include indexed union. Note: Historically (prior to 21-Oct-2005), used the notation  U. x  e.  A B, with the same union symbol as cuni 3973. While that syntax was unambiguous, it did not allow for LALR parsing of the syntax constructions in The new syntax uses as distinguished symbol  U_ instead of  U. and does allow LALR parsing. Thanks to Peter Backes for suggesting this change.
Ref Expression
vx  set  x
cA  class  A
cB  class  B
Ref Expression
ciun  class  U_ x  e.  A  B

See definition df-iun 4053 for more information.

Colors of variables: wff set class
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