.decl A(text: symbol)
.decl B(text: symbol)
.decl SymmetricDifference(text: symbol)
.output SymmetricDifference

A("this").
A("is").
A("a").
A("test").
B("also").
B("part").
B("of").
B("a").
B("test").

SymmetricDifference(x) :- A(x), !B(x).
SymmetricDifference(x) :- B(x), !A(x).