protected override bool KBEntails(Block ask)
{
// only true if input symbols are Horn clauses but in disjunctive form
var symbol = ask.GetContent(true).ToString();
if (!Path.Contains(symbol))
{
Path.Insert(0, symbol);
}
if (HornClauses.IsFact(symbol))
{
return(true);
}
var relatedSymbols = HornClauses.GetClause(symbol);
// terminable because this is the end of the chain but no facts found
if (relatedSymbols == null)
{
return(false);
}
bool result = false;
foreach (var relatedList in relatedSymbols)
{
bool innerResult = false, firstValue = false;
foreach (var s in relatedList)
{
if (!firstValue)
{
firstValue = true;
innerResult = KBEntails(new Block(s));
continue;
}
innerResult &= KBEntails(new Block(s));
}
// one innerResult equals to true means that
// this symbol is indeed a fact without anymore consideration
result |= innerResult;
}
if (result)
{
HornClauses.Facts.Add(symbol);
}
return(result);
}
public override string Prove(KnowledgeBase kb, string ask)
{
HornClauses = new HornClauses(kb.Knowledges);
base.Prove(kb, ask);
return(KBEntails(ClauseParser.Parse(ask)) ? $"YES: {string.Join(", ", Path)}" : "NO");
}