Set Types  77  S.A.  Set Constructors  Figure S.b  Syntax diagram for  SetConstructor  Examples of 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.  [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']  Expression  f--~--"'-.,. 