Syntax Definition ciun 3969

Description: Extend class notation to include indexed union. Note: Historically (prior to 21-Oct-2005), set.mm used the notation ∪x ∈ AB, with the same union symbol as cuni 3891. 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 ∪ instead of ∪ and does allow LALR parsing. Thanks to Peter Backes for suggesting this change.

Hypotheses

Ref	Expression
vx	setvar x
cA	class A
cB	class B

Assertion

Ref	Expression
ciun	class ∪x ∈ A B

See definition df-iun 3971 for more information.