// <summary>
// Retrieves all implications directly derivable from the atomic expression.
// </summary>
// <param name="expression">
// Atomic expression to be extended with facts derivable from the knowledge base.
// </param>
internal DomainBoolExpr Chase(DomainTermExpr expression)
{
DomainBoolExpr implication;
Implications.TryGetValue(expression, out implication);
return(new AndExpr <DomainConstraint>(expression, implication ?? TrueExpr <DomainConstraint> .Value));
}
public HornClauses(List <Block> clauses) : this()
{
foreach (var clause in clauses)
{
if (clause.NextBlock == clause && clause.PreviousBlock == clause)
{
Facts.Add(clause.GetContent(true).ToString());
continue;
}
// safe against nested symbols inside clause or multiple clauses pointing at 1 symbol
var symbol = clause.PreviousBlock.GetContent(true).ToString();
var unvisited = new List <Block> {
clause
};
if (!Implications.ContainsKey(symbol))
{
Implications.Add(symbol, new List <List <string> >());
}
// if a horn clause is pointing at the same symbol as some other horn clauses,
// add current clause's requirements to a new list instead of combining them together
Implications[symbol].Add(new List <string>());
// recursion using while loop, flatten down all nested symbols (if any)
// as well as pushing clause's requirements for future reference
while (unvisited.Count != 0)
{
BlockIterator.TerminableForEach(unvisited[0], (block) =>
{
switch (block.ContentType)
{
case ContentType.Logic:
if ((block.GetContent() as PropositionalLogic).IsImplication)
{
return(false);
}
break;
case ContentType.Normal:
Implications[symbol].Last().Add(block.GetContent(true).ToString());
break;
case ContentType.Nested:
unvisited.Add(block.GetContent() as Block);
break;
}
return(true);
});
unvisited.RemoveAt(0);
}
}
}
public static bool Infers <T>(this T premise, T conclusion, Paradox <T> predicate = null)
{
if (null == predicate)
{
return(premise.Implies(conclusion, Infers));
}
if (Implies != predicate)
{
return(predicate(premise, conclusion));
}
return(Implications.CheckImplies(premise, conclusion));
}
