| ?- sat(X + Y). sat(X=\=_A*Y#Y)
illustrates three facts. First, any accumulated constraints affecting
the top-level variables are displayed floundered
goals, since the query is not true for all
Y. Secondly, accumulated constraints are displayed as
where V is a variable and Expr is a “polynomial”,
i.e. an exclusive or of conjunctions of variables and
_A had to be introduced as an artificial
Y cannot be expressed as a function of
X. That is,
X + Y is true iff there exists an
X=\=_A*Y#Y. Let’s check it!
| ?- taut(_A ^ (X=\=_A*Y#Y) =:= X + Y, T). T = 1
verifies the above answer. Notice that the formula in this query is a tautology, and so it is entailed by an empty set of constraints.