Unions

Set unions can be formed using an addition type operation namely (setarith.gms)

Subset3(superset) = Subset1(superset) + Subset2(superset);

The membership of subset3 contains all elements that are either members of subset1 and or subset2. This operation is equivalent to the statements

Subset3(superset)=no; subset3(subset1)=yes; subset3(subset2)=yes;