private static Implication RemoveNotDistinctLiteral(Implication rule, Negation notDistinctLiteral)
{
//Figure out the substitution we want...
//If we have two constantsin Either Remove one or
//maybe get rid of the ___?
//One is a variablein Replace the variable with the other thing
//throughout the rule
var distinct = (Fact)notDistinctLiteral.Negated;
Term arg1 = distinct.GetTerm(0);
Term arg2 = distinct.GetTerm(1);
if (arg1 == arg2)
{
//Just Remove that literal
var newBody = new List<Expression>();
newBody.AddRange(rule.Antecedents.Conjuncts);
newBody.Remove(notDistinctLiteral);
return new Implication(rule.Consequent, newBody.ToArray());
}
var p1 = arg1 as TermVariable;
if (p1 != null)
{
//What we return will still have the not-distinct literal,
//but it will get replaced in the next pass.
//(Even if we have two variables, they will be equal next time through.)
var sub = new Substitution();
sub.AddMapping(p1, arg2);
return (Implication)rule.ApplySubstitution(sub);
}
var variable = arg2 as TermVariable;
if (variable != null)
{
var sub = new Substitution();
sub.AddMapping(variable, arg1);
return (Implication)rule.ApplySubstitution(sub);
}
if (arg1 is TermObject || arg2 is TermObject)
{
//We have two non-equal constants, or a constant and a function.
//The rule should have no effect.
return null;
}
//We have two functions. Complicated! (Have to replace them with unified version.)
//We pass on this case for now.
//TODO: Implement correctly.
throw new Exception("We can't currently handle (not (distinct <function> <function>)).");
}
private static void VisitNot(Negation not, GdlVisitor visitor)
{
visitor.VisitNot(not);
VisitAll(not.Negated, visitor);
}
private static Substitution Mgu(Negation neg1, Negation neg2)
{
return Mgu(neg1.Negated, neg2.Negated);
}
private static Negation SubstituteNot(Negation not, Substitution theta)
{
return not.VariablesOrEmpty.Any()
? new Negation(SubstituteLiteral(not.Negated, theta))
: not;
}
private Negation RenameNot(Negation not, Dictionary<TermVariable, TermVariable> renamings)
{
return not.VariablesOrEmpty.Any()
? new Negation(RenameLiteral(not.Negated, renamings))
: not;
}
private void AskNot(Negation not, LinkedList<Expression> goals, KnowledgeBase context, Substitution theta, ProverCache cache,
VariableRenamer renamer, bool askOne, HashSet<Substitution> results, HashSet<Fact> alreadyAsking)
{
var notGoals = new LinkedList<Expression>();
notGoals.AddLast(not.Negated);
var notResults = new HashSet<Substitution>();
Ask(notGoals, context, theta, cache, renamer, true, notResults, alreadyAsking);
if (notResults.Count == 0)
Ask(goals, context, theta, cache, renamer, askOne, results, alreadyAsking);
}
