private void ApplyDoubleNegationRule(Proposition proposition)
{
HashSet <Proposition> propositions = new HashSet <Proposition>();
foreach (Proposition p in Propositions)
{
if (!p.Equals(proposition))
{
propositions.Add(p);
}
}
Proposition doubleNegationRemoved = null;
if (proposition.GetType() == typeof(Negation))
{
Negation negation = (Negation)proposition;
Proposition negatedProposition = negation.LeftSuccessor;
if (negatedProposition.GetType() == typeof(Negation))
{
Negation negatedNegation = (Negation)negatedProposition;
doubleNegationRemoved = negatedNegation.LeftSuccessor;
propositions.Add(doubleNegationRemoved);
}
}
LeftChild = new SemanticTableauxElement(propositions, new HashSet <char>(ReplacementVariables));
}
private static void NumberElements(SemanticTableaux semanticTableaux)
{
List <SemanticTableauxElement> queue = new List <SemanticTableauxElement>();
queue.Add(semanticTableaux.Head);
int nodeCounter = 1;
SemanticTableauxElement currentElement = null;
while (queue.Count > 0)
{
currentElement = queue[0];
queue.RemoveAt(0);
currentElement.NodeNumber = nodeCounter;
if (currentElement.LeftChild != null)
{
queue.Add(currentElement.LeftChild);
}
if (currentElement.RightChild != null)
{
queue.Add(currentElement.RightChild);
}
nodeCounter++;
}
}
public SemanticTableaux(Proposition proposition)
{
Proposition = proposition;
if (proposition == null)
{
throw new NullReferenceException("A proposition is required to make use of the semantic tableaux");
}
Negation negation = new Negation();
negation.LeftSuccessor = proposition;
HashSet <Proposition> propositions = new HashSet <Proposition>()
{
negation
};
// Then the type of semantic tableaux element could be
// set by the semantic tableaux by perhaps setting
// an enum on the semantic tableaux element
// which calls a create method
SemanticTableauxElement.ResetReplacementVariables();
Head = new SemanticTableauxElement(propositions);
}
private void ApplyAlphaRule(Proposition proposition)
{
HashSet <Proposition> childPropositions = new HashSet <Proposition>();
foreach (Proposition p in Propositions)
{
if (!p.Equals(proposition))
{
childPropositions.Add(p);
}
}
if (proposition.GetType() == typeof(Conjunction))
{
BinaryConnective connective = (BinaryConnective)proposition;
childPropositions.Add(connective.LeftSuccessor);
childPropositions.Add(connective.RightSuccessor);
}
if (proposition.GetType() == typeof(Negation))
{
Negation negation = (Negation)proposition;
BinaryConnective nestedConnective = (BinaryConnective)negation.LeftSuccessor;
if (nestedConnective.GetType() != typeof(Nand))
{
// Both cases have a negation of the right successor.
Negation negatedRight = new Negation();
negatedRight.LeftSuccessor = nestedConnective.RightSuccessor;
// Only disjunction results in a left side negated as well.
if (nestedConnective.GetType() == typeof(Disjunction))
{
Negation negatedLeft = new Negation();
negatedLeft.LeftSuccessor = nestedConnective.LeftSuccessor;
childPropositions.Add(negatedLeft);
}
// Should not forget to add the implication's left successor
if (nestedConnective.GetType() == typeof(Implication))
{
childPropositions.Add(nestedConnective.LeftSuccessor);
}
childPropositions.Add(negatedRight);
}
else
{
// It's a negated Nand and we can add left and right to the set
childPropositions.Add(nestedConnective.LeftSuccessor);
childPropositions.Add(nestedConnective.RightSuccessor);
}
}
LeftChild = new SemanticTableauxElement(childPropositions, new HashSet <char>(ReplacementVariables));
}
private void ApplyDeltaRule(Proposition proposition)
{
// COULD BE: GetAllDifferingChildPropositions(proposition)
// REFACTOR WORTHY: otherwise needs to be tested for every rule which is all the same
HashSet <Proposition> childPropositions = new HashSet <Proposition>();
foreach (Proposition p in Propositions)
{
if (!p.Equals(proposition))
{
childPropositions.Add(p);
}
}
// REFACTOR WORTHY
// Current proposition we want to break up again into new pieces.
Quantifier quantifier = null;
Proposition predicate = null;
if (proposition.GetType() == typeof(Negation))
{
Negation negatedUniversalQuantifier = (Negation)proposition;
quantifier = (Quantifier)negatedUniversalQuantifier.LeftSuccessor;
predicate = quantifier.LeftSuccessor;
Negation negatedPredicate = new Negation();
negatedPredicate.LeftSuccessor = predicate;
predicate = negatedPredicate;
}
else
{
quantifier = (Quantifier)proposition;
predicate = quantifier.LeftSuccessor;
}
char boundVariable = quantifier.GetBoundVariable();
char replacementCharacter = GenerateReplacementVariable();
Proposition predicateCopy = predicate.Copy();
predicateCopy.Replace(boundVariable, replacementCharacter);
// Get current set locally, add new variable and pass them down.
HashSet <char> childReplacementVariables = new HashSet <char>(ReplacementVariables);
childReplacementVariables.Add(replacementCharacter);
childPropositions.Add(predicateCopy);
LeftChild = new SemanticTableauxElement(childPropositions, childReplacementVariables);
}
private void ApplyBetaRule(Proposition proposition)
{
HashSet <Proposition> leftChildPropositions = new HashSet <Proposition>();
HashSet <Proposition> rightChildPropositions = new HashSet <Proposition>();
Proposition leftSetProposition = null;
Proposition rightSetPropostion = null;
foreach (Proposition p in Propositions)
{
if (!p.Equals(proposition))
{
// Add copies to the set for all other propositions
// ensuring that each quantifier will at least be unique.
leftChildPropositions.Add(p.Copy());
rightChildPropositions.Add(p.Copy());
}
}
BinaryConnective connective = null;
if (proposition.GetType() == typeof(Negation) || proposition.GetType() == typeof(Nand))
{
Negation leftNegation = new Negation();
Negation rightNegation = new Negation();
// Possibly Not and or Not bi-implication
if (proposition.GetType() == typeof(Negation))
{
Negation negation = (Negation)proposition;
connective = (BinaryConnective)negation.LeftSuccessor;
// If Bi-Implication
if (connective.GetType() == typeof(BiImplication))
{
leftChildPropositions.Add(connective.LeftSuccessor);
leftNegation.LeftSuccessor = connective.RightSuccessor;
rightChildPropositions.Add(connective.RightSuccessor);
rightNegation.LeftSuccessor = connective.LeftSuccessor;
}
else
{
// If And
leftNegation.LeftSuccessor = connective.LeftSuccessor;
rightNegation.LeftSuccessor = connective.RightSuccessor;
}
}
else
{
// If Nand
connective = (BinaryConnective)proposition;
leftNegation.LeftSuccessor = connective.LeftSuccessor;
rightNegation.LeftSuccessor = connective.RightSuccessor;
}
leftSetProposition = leftNegation;
rightSetPropostion = rightNegation;
}
if (proposition.GetType() == typeof(Disjunction))
{
connective = (BinaryConnective)proposition;
leftSetProposition = connective.LeftSuccessor;
rightSetPropostion = connective.RightSuccessor;
}
if (proposition.GetType() == typeof(Implication))
{
Negation leftNegation = new Negation();
connective = (BinaryConnective)proposition;
leftNegation.LeftSuccessor = connective.LeftSuccessor;
leftSetProposition = leftNegation;
rightSetPropostion = connective.RightSuccessor;
}
if (proposition.GetType() == typeof(BiImplication))
{
connective = (BinaryConnective)proposition;
Negation leftNegated = new Negation();
leftNegated.LeftSuccessor = connective.LeftSuccessor;
Negation rightNegated = new Negation();
rightNegated.LeftSuccessor = connective.RightSuccessor;
// First add the left part of the bi-implication to both left and right branch
// sets
leftChildPropositions.Add(connective.LeftSuccessor);
rightChildPropositions.Add(leftNegated);
// Then the right part to keep a certain order.
leftSetProposition = connective.RightSuccessor;
rightSetPropostion = rightNegated;
}
leftChildPropositions.Add(leftSetProposition);
rightChildPropositions.Add(rightSetPropostion);
LeftChild = new SemanticTableauxElement(leftChildPropositions, new HashSet <char>(ReplacementVariables));
RightChild = new SemanticTableauxElement(rightChildPropositions, new HashSet <char>(ReplacementVariables));
}
// Both, just the ordering is different and for predicates we
// have two additional rules that should be placed in between.
protected void CreateChildren()
{
bool childCreated = false;
foreach (Proposition proposition in Propositions)
{
childCreated = TryToCreateDoubleNegation(proposition);
if (childCreated)
{
return;
}
}
foreach (Proposition proposition in Propositions)
{
childCreated = TryToCreateAlphaRule(proposition);
if (childCreated)
{
return;
}
}
foreach (Proposition proposition in Propositions)
{
childCreated = TryToCreateDeltaRule(proposition);
if (childCreated)
{
return;
}
}
foreach (Proposition proposition in Propositions)
{
childCreated = TryToCreateBetaRule(proposition);
if (childCreated)
{
return;
}
}
HashSet <Proposition> childPropositionSet = new HashSet <Proposition>();
foreach (Proposition proposition in Propositions)
{
if (IsGammaRule(proposition))
{
foreach (Proposition p in ApplyGammaRule(proposition))
{
childPropositionSet.Add(p);
}
}
}
if (childPropositionSet.Count > Propositions.Count)
{
LeftChild = new SemanticTableauxElement(childPropositionSet, ReplacementVariables);
return;
}
}