Syntax Definition ciun 4520

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 4436. While that syntax was unambiguous, it did not allow for LALR parsing of the syntax constructions in set.mm. The new syntax uses a distinguished symbol U_ instead of U. 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 U_ x e. A B

See definition df-iun 4522 for more information.