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## S.A. Set Constructors 

A set value can be specified by a set constructor which contains descriptions of the set elements separated by commas and enclosed in square brackets. An element description can be an expression, the value of which is the element, or a range of the form low .. high, where the values of the expressions low and high are the lower and upper bounds of a collection of elements. If the lower bound is greater than the upper bound of the range (i.e., low> high), no elements are described. 

The expressions must all have the same ordinal type which is the base type of the set constructor type. The set constructor [ ] denotes the empty set of every set type. Set constructors do not carry full type information [see Reference 10], such as whether ornotthe set is packed. Therefore the type of a set constructor is both packed and unpacked to be type compatible with other sets in set expressions. 

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Examples of set constructors: 

[13] [i+j,i-j] [' 0' .. ' 9' ] [red, yellow, blue] ['a' ,'b' ,'e' I'd' ,'e' ,'f' f'g' ,'h' ,'i', 'j' ,'k' ,'1' ,'m' ,'n' ,'0' ,'p' ,'q' ,'r', 's' ,'t' ,'U' ,'v' ,'w' ,'x' ,'y' ,'z'] 

