testSolutionWithDandlingVars

Tests the query

?- append(A, B).

against the fact append(seq(X), X).; succeeds binding A to seq(X) (a fresh renaming of the fact's own X) and B to that same fresh variable, and checks that both A and B are present in the returned substitution's keys — including B, whose "value" is itself a dangling variable (named X) rather than a ground term.