/// <summary>
/// <code> function INFER(clause, usable) returns clauses </code>
/// </summary>
/// <param name="clause"></param>
/// <param name="usable"></param>
/// <returns></returns>
private ISet<Clause> Infer(Clause clause, ISet<Clause> usable)
{
ISet<Clause> resultingClauses = new HashedSet<Clause>();
// * resolve clause with each member of usable
foreach (var c in usable)
{
ISet<Clause> resolvents = clause.BinaryResolvents(c);
foreach (Clause rc in resolvents)
{
resultingClauses.Add(rc);
}
// if using paramodulation to handle equality
if (this.UseParamodulation)
{
var paras = paramodulation.Apply(clause, c, true);
foreach (var p in paras)
{
resultingClauses.Add(p);
}
}
}
// * return the resulting clauses after applying filter
return ClauseFilter.Filter(resultingClauses);
}
public IInferenceResult Ask(FOLKnowledgeBase kb, ISentence alpha)
{
// clauses <- the set of clauses in CNF representation of KB ^ ~alpha
ISet <Clause> clauses = new HashedSet <Clause>();
foreach (Clause c in kb.GetAllClauses())
{
var standardizedC = kb.StandardizeApart(c);
standardizedC.SetStandardizedApartCheckNotRequired();
clauses.UnionWith(standardizedC.GetFactors());
}
ISentence notAlpha = new NotSentence(alpha);
// Want to use an answer literal to pull
// query variables where necessary
Literal answerLiteral = kb.CreateAnswerLiteral(notAlpha);
ISet <Variable> answerLiteralVariables = kb
.CollectAllVariables(answerLiteral.AtomicSentence);
Clause answerClause = new Clause();
if (answerLiteralVariables.Count > 0)
{
ISentence notAlphaWithAnswer = new ConnectedSentence(Connectors.Or,
notAlpha, answerLiteral.AtomicSentence);
foreach (Clause c in kb.ConvertToClauses(notAlphaWithAnswer))
{
var standardizedC = kb.StandardizeApart(c);
standardizedC.SetProofStep(new ProofStepGoal(standardizedC));
standardizedC.SetStandardizedApartCheckNotRequired();
clauses.UnionWith(standardizedC.GetFactors());
}
answerClause.AddLiteral(answerLiteral);
}
else
{
foreach (Clause c in kb.ConvertToClauses(notAlpha))
{
var standardizedC = kb.StandardizeApart(c);
standardizedC.SetProofStep(new ProofStepGoal(standardizedC));
standardizedC.SetStandardizedApartCheckNotRequired();
clauses.UnionWith(standardizedC.GetFactors());
}
}
var ansHandler = new TFMAnswerHandler(answerLiteral,
answerLiteralVariables, answerClause, this.MaxQueryTime);
// new <- {}
ISet <Clause> newClauses = new HashedSet <Clause>();
ISet <Clause> toAdd = new HashedSet <Clause>();
// loop do
int noOfPrevClauses = clauses.Count;
do
{
if (Tracer != null)
{
Tracer.StepStartWhile(clauses, clauses.Count, newClauses
.Count);
}
newClauses.Clear();
// for each Ci, Cj in clauses do
Clause[] clausesA = new Clause[clauses.Count];
clausesA = clauses.ToArray();
// Basically, using the simple T)wo F)inger M)ethod here.
for (int i = 0; i < clausesA.Length; i++)
{
Clause cI = clausesA[i];
if (null != Tracer)
{
Tracer.StepOuterFor(cI);
}
for (int j = i; j < clausesA.Length; j++)
{
Clause cJ = clausesA[j];
if (null != Tracer)
{
Tracer.StepInnerFor(cI, cJ);
}
// resolvent <- FOL-RESOLVE(Ci, Cj)
ISet <Clause> resolvents = cI.BinaryResolvents(cJ);
if (resolvents.Count > 0)
{
toAdd.Clear();
// new <- new <UNION> resolvent
foreach (Clause rc in resolvents)
{
toAdd.UnionWith(rc.GetFactors());
}
if (null != Tracer)
{
Tracer.StepResolved(cI, cJ, toAdd);
}
ansHandler.CheckForPossibleAnswers(toAdd);
if (ansHandler.IsComplete())
{
break;
}
newClauses.UnionWith(toAdd);
}
if (ansHandler.IsComplete())
{
break;
}
}
if (ansHandler.IsComplete())
{
break;
}
}
noOfPrevClauses = clauses.Count;
// clauses <- clauses <UNION> new
clauses.UnionWith(newClauses);
if (ansHandler.IsComplete())
{
break;
}
// if new is a <SUBSET> of clauses then finished
// searching for an answer
// (i.e. when they were added the # clauses
// did not increase).
} while (noOfPrevClauses < clauses.Count);
if (null != Tracer)
{
Tracer.StepFinished(clauses, ansHandler);
}
return(ansHandler);
}
