[LOGIC-100] pruning of unsatisfiable non-ground disequalities

Mon, 7 Jan 2013 11:00:06 -0600

Not sure whether we actually want to do anything about this.

When running this snippet,

(run* [q]
  (fresh [a b]
    (== q [a b])
    (!= a q)))

we get the result:

(([_0 _1] :- (!= (_0 [_0 _1]))))

The reified != constraint is arguably spurious, because of the occurs-check.

Even if we instantiate the a:

(run* [q]
  (fresh [a b]
    (== q [a b])
    (!= a q)
    (== a 1)))

we get the result:

(([1 _0] :- (!= (1 [1 _0]))))

while there is no way the != constraint can be satisfied.

Thoughts?

Clojure JIRA