# HeaderType -- a class of lists with abbreviated constructors

## Description

These are the types X of lists that can be constructed by expressions of the form X {a,b,c,...}. They also act on sequences.

 i1 : X = new HeaderType of BasicList o1 = X o1 : HeaderType i2 : X {a,b,c} o2 = X{a, b, c} o2 : X