Me too. I might be abusing the term. I am saying in the sense of
free variables or unbounded variables in the lambda calculus.
Your comment on double negations sound positive for me, who is too familiar with using “!” , and “!, fail”. “One should get familiar with using “!” to write a good prolog codes like a good barber is so with his shaving cutters” I was told like this by an influential scholar who introduced Prolog to Japan in earlier time.