Syntax	An indexType is one of:   (a) subrangeType   (b) enumeratedType   (c) namedType   % Which is a subrange or enumerated type   (d) char   (e) boolean
Description	An index type defines a range of values that can be used as an array subscript, as a case selector, as a selector (tag) for a union type, or as the base type of a set type.
Example	var z : array 1 .. 9 of real % 0..9 is an index type type smallSet : set of 0 .. 2 % 0..2 is an index type