A Maths_atom is a Maths_value that is a Boolean, complex, integer, or real value.
NOTE - For efficiency Maths_value is a TYPE rather than and ENTITY in the EXPRESS. Hence Maths_atom is referenced by Maths_value rather than a SUBTYPE of Maths_value.
EXPRESS specification:
*) TYPE Maths_atom = SELECT ( Maths_boolean, Maths_complex, Maths_integer, Maths_real); END_TYPE; (*