A Maths_tuple is a Maths_value that is a tuple of instances of Maths_value.
NOTE - For efficiency Maths_value is a TYPE rather than and ENTITY in the EXPRESS. Hence Maths_tuple is referenced by Maths_value rather than a SUBTYPE of Maths_value.
EXPRESS specification:
*) TYPE Maths_tuple = LIST [2,?] OF Maths_value; END_TYPE; (*