public static FormulaNode JoinTerms(LogicOperator op, List <FormulaNode> terms)
{
FormulaNode result;
if (terms.Count == 0)
{
if (op == LogicOperator.AND)
{
return(new FormulaNode(FormulaNode.TRUE_LITERAL));
}
if (op == LogicOperator.OR)
{
// Build FALSE as ~TRUE
result = new FormulaNode(LogicOperator.NOT);
result.SetChildren(new FormulaNode(FormulaNode.TRUE_LITERAL), null);
return(result);
}
throw new Exception("Join with unsupported logic operator");
}
if (terms.Count == 1)
{
return(terms[0]);
}
result = new FormulaNode(op, terms[0], terms[1]);
foreach (var t in terms.GetRange(2, terms.Count - 2))
{
result = new FormulaNode(op, result, t);
}
return(result);
}
public static FormulaNode nnfNegate(FormulaNode formula)
{
FormulaNode result = new FormulaNode(LogicOperator.NOT);
result.SetChildren(formula, null);
return(result.NNF());
}
/* Generates a formula representing the fact that for <state> either
* the eventuality is not promised or that if it is, then there
* exists a fragment of <stateSet> rooted at <state> that has
* a frontier node who satisfied the eventuallity
*/
private FormulaNode GenE(FormulaNode stateSet, SymbolicState state)
{
ComputeEUFragments(stateSet, state);
List <FormulaNode> terms = new List <FormulaNode>();
foreach (var e in elementary)
{
if (e.GetLogicOperator() != LogicOperator.EX)
{
continue;
}
if (e[0].GetLogicOperator() != LogicOperator.EU)
{
continue;
}
FormulaNode notPromised = new FormulaNode(LogicOperator.NOT);
notPromised.SetChildren(state.ValueOf(e), null);
FormulaNode res = new FormulaNode(LogicOperator.OR);
res.SetChildren(notPromised, new FormulaNode(LogicOperator.NOT));
res[1].SetChildren(state.ValueOf(e[0][0]), null);
FormulaNode frag = fragEU[e[0]];
res = new FormulaNode(LogicOperator.OR, res, frag);
terms.Add(res);
}
return(JoinTerms(LogicOperator.AND, terms));
}
public static FormulaNode CreateTestFormula()
{
FormulaNode result = new FormulaNode(LogicOperator.EX);
result.SetChildren(null, new FormulaNode("b"));
result = new FormulaNode(LogicOperator.EU);
FormulaNode a = new FormulaNode(LogicOperator.AG);
a.SetChildren(new FormulaNode("p"), null);
result.SetChildren(a, new FormulaNode("q"));
return(result);
}
/* Replace the variables describing the state <from> with the ones that describe
* state <to>
*/
public static FormulaNode Substitute(FormulaNode formula, SymbolicState from, SymbolicState to)
{
if (formula.GetLogicOperator() == LogicOperator.VAR)
{
if (from.nameToElementary.Keys.Contains(formula.GetName()))
{
// this variable represents an elementary formula
var elementary = from.nameToElementary[formula.GetName()];
return(new FormulaNode(to.elementaryNames[elementary]));
}
else
{
return(new FormulaNode(formula.GetName()));
}
}
if (formula.GetLogicOperator() == LogicOperator.ALL ||
formula.GetLogicOperator() == LogicOperator.EXISTS)
{
FormulaNode result = new FormulaNode(formula.GetLogicOperator());
if (from.nameToElementary.Keys.Contains(formula.GetName()))
{
// this variable represents an elementary formula
var elementary = from.nameToElementary[formula.GetName()];
result.SetName(to.elementaryNames[elementary]);
}
else
{
result.SetName(formula.GetName());
}
result.SetChildren(Substitute(formula[0], from, to), null);
return(result);
}
FormulaNode res = new FormulaNode(formula.GetLogicOperator());
FormulaNode left = Substitute(formula[0], from, to);
FormulaNode right = null;
if (formula[1] != null)
{
right = Substitute(formula[1], from, to);
}
res.SetChildren(left, right);
return(res);
}
// replace ->, AF, AG, EF and EG with simpler operators
public FormulaNode ImplementComplexOperators()
{
FormulaNode leftChild = null;
FormulaNode rightChild = null;
FormulaNode trueFormula = new FormulaNode(TRUE_LITERAL);
FormulaNode falseFormula = new FormulaNode(LogicOperator.NOT, trueFormula, null);
FormulaNode result;
if (this[0] != null)
{
leftChild = this[0].ImplementComplexOperators();
}
if (this[1] != null)
{
rightChild = this[1].ImplementComplexOperators();
}
switch (logicOp)
{
// (a -> b) is (~a | b)
case LogicOperator.IMP:
FormulaNode left = new FormulaNode(LogicOperator.NOT, leftChild, null);
return(new FormulaNode(LogicOperator.OR, left, rightChild));
// EF(f) is EU(TRUE, f)
case LogicOperator.EF:
return(new FormulaNode(LogicOperator.EU, trueFormula, leftChild));
// EG(f) is ER(FALSE, f)
case LogicOperator.EG:
return(new FormulaNode(LogicOperator.ER, falseFormula, leftChild));
// AF(f) is AU(TRUE, f)
case LogicOperator.AF:
return(new FormulaNode(LogicOperator.AU, trueFormula, leftChild));
// AG(f) is AU(FALSE, f)
case LogicOperator.AG:
return(new FormulaNode(LogicOperator.AR, falseFormula, leftChild));
default:
result = new FormulaNode(logicOp, name);
result.SetChildren(leftChild, rightChild);
return(result);
}
}
// Change f[x] to f[x/x']
public FormulaNode Substitute(string original, string replacement)
{
if (this.logicOp == LogicOperator.VAR)
{
if (this.name == original)
{
return(new FormulaNode(replacement));
}
else
{
return(new FormulaNode(this.name));
}
}
FormulaNode res = new FormulaNode(this.logicOp, this.name);
if ((this.logicOp == LogicOperator.EXISTS ||
this.logicOp == LogicOperator.ALL) &&
(this.name == original))
{
res.name = replacement;
}
FormulaNode left = null, right = null;
if (this.childNodes[0] != null)
{
left = this.childNodes[0].Substitute(original, replacement);
}
if (this.childNodes[1] != null)
{
right = this.childNodes[1].Substitute(original, replacement);
}
res.SetChildren(left, right);
return(res);
}
/* Assumes the formula is in NNF form */
public static ISet <FormulaNode> elementaryFormulas(FormulaNode formula)
{
HashSet <FormulaNode> result = new HashSet <FormulaNode>();
switch (formula.GetLogicOperator())
{
case LogicOperator.AU:
case LogicOperator.AR:
// AX(f) is elementary
FormulaNode ax_f = new FormulaNode(LogicOperator.AX);
ax_f.SetChildren(formula, null);
result.Add(ax_f);
result.Add(nnfNegate(ax_f));
result.UnionWith(elementaryFormulas(formula[0]));
result.UnionWith(elementaryFormulas(formula[1]));
break;
case LogicOperator.EU:
case LogicOperator.ER:
// EX(f) is elementary
FormulaNode ex_f = new FormulaNode(LogicOperator.EX);
ex_f.SetChildren(formula, null);
result.Add(ex_f);
result.Add(nnfNegate(ex_f));
result.UnionWith(elementaryFormulas(formula[0]));
result.UnionWith(elementaryFormulas(formula[1]));
break;
case LogicOperator.EX:
case LogicOperator.AX:
// the formula itself is elementary
result.Add(formula);
result.Add(nnfNegate(formula));
result.UnionWith(elementaryFormulas(formula[0]));
break;
case LogicOperator.OR:
case LogicOperator.AND:
result.UnionWith(elementaryFormulas(formula[0]));
result.UnionWith(elementaryFormulas(formula[1]));
break;
case LogicOperator.NOT:
Debug.Assert(formula[0].GetLogicOperator() == LogicOperator.VAR,
"Input to elementaryFormulas must be in NNF form");
result.UnionWith(elementaryFormulas(formula[0]));
break;
case LogicOperator.VAR:
if (formula.GetName() != FormulaNode.TRUE_LITERAL)
{
result.Add(formula);
result.Add(nnfNegate(formula));
}
break;
default:
throw new Exception("Not implemented");
}
return(result);
}
// Trnasfer the node to PNF (the formula is assumed to be in NNF)
// We assume that the formula also has no temporal operators
public FormulaNode PNF()
{
if (this.logicOp == LogicOperator.VAR)
{
return(new FormulaNode(this.name));
}
FormulaNode res = null, left = null, right = null;
ISet <string> leftSet, rightSet;
string varname;
if (this.logicOp == LogicOperator.NOT)
{
res = new FormulaNode(LogicOperator.NOT);
res.SetChildren(new FormulaNode(this.childNodes[0].name), null);
return(res);
}
if (this.logicOp == LogicOperator.EXISTS ||
this.logicOp == LogicOperator.ALL)
{
res = new FormulaNode(this.logicOp, this.name);
res.SetChildren(this.childNodes[0].PNF(), null);
return(res);
}
// Since we assume NNF, all NOT nodes are next to variables
// Thus all of the remaining operators are binary
left = this.childNodes[0].PNF();
right = this.childNodes[1].PNF();
leftSet = left.GetVariables();
rightSet = right.GetVariables();
if (this.logicOp == LogicOperator.AND ||
this.logicOp == LogicOperator.OR)
{
FormulaNode temp;
if (left.logicOp == LogicOperator.EXISTS ||
left.logicOp == LogicOperator.ALL)
{
if (rightSet.Contains(left.name))
{
varname = UniquePNFVariable();
left = left.Substitute(left.name, varname);
}
res = new FormulaNode(left.logicOp, left.name);
temp = new FormulaNode(this.logicOp);
temp.SetChildren(left.childNodes[0], right);
res.SetChildren(temp.PNF(), null);
}
else if (right.logicOp == LogicOperator.EXISTS ||
right.logicOp == LogicOperator.ALL)
{
if (leftSet.Contains(right.name))
{
varname = UniquePNFVariable();
right = right.Substitute(right.name, varname);
}
res = new FormulaNode(right.logicOp, right.name);
temp = new FormulaNode(this.logicOp);
temp.SetChildren(left, right.childNodes[0]);
res.SetChildren(temp.PNF(), null);
}
else
{
res = new FormulaNode(this.logicOp);
res.SetChildren(left, right);
}
}
// For convenience, we get rid of "->" operators
if (this.logicOp == LogicOperator.IMP)
{
res = new FormulaNode(LogicOperator.OR);
res.SetChildren(new FormulaNode(LogicOperator.NOT), right);
res.childNodes[0].SetChildren(left, null);
res = res.NNF().PNF();
}
return(res);
}
// Transfer the node to NNF
public FormulaNode NNF()
{
if (this.logicOp == LogicOperator.VAR)
{
return(new FormulaNode(this.name));
}
FormulaNode res = null, left = null, right = null;
if (this.logicOp != LogicOperator.NOT)
{
res = new FormulaNode(this.logicOp, this.name);
if (this.childNodes[0] != null)
{
left = this.childNodes[0].NNF();
}
if (this.childNodes[1] != null)
{
right = this.childNodes[1].NNF();
}
res.SetChildren(left, right);
return(res);
}
// If we reached here, our node is "~" and hence we should
// rearrange the formula tree
// We note that a "~" should be unary and hence it only
// has a left child
switch (this.childNodes[0].logicOp)
{
case LogicOperator.EXISTS:
res = new FormulaNode(LogicOperator.ALL, this.childNodes[0].name);
break;
case LogicOperator.ALL:
res = new FormulaNode(LogicOperator.EXISTS, this.childNodes[0].name);
break;
case LogicOperator.AND:
res = new FormulaNode(LogicOperator.OR);
break;
case LogicOperator.OR:
res = new FormulaNode(LogicOperator.AND);
break;
case LogicOperator.NOT:
return(this.childNodes[0].childNodes[0].NNF());
case LogicOperator.IMP:
// ~(a->b) == a & ~b
res = new FormulaNode(LogicOperator.AND);
left = this.childNodes[0].childNodes[0].NNF();
right = new FormulaNode(LogicOperator.NOT);
right.SetChildren(this.childNodes[0].childNodes[1].NNF(), null);
res.SetChildren(left, right.NNF());
return(res);
case LogicOperator.EF:
res = new FormulaNode(LogicOperator.AG);
break;
case LogicOperator.AF:
res = new FormulaNode(LogicOperator.EG);
break;
case LogicOperator.EG:
res = new FormulaNode(LogicOperator.AF);
break;
case LogicOperator.AG:
res = new FormulaNode(LogicOperator.EF);
break;
case LogicOperator.AX:
res = new FormulaNode(LogicOperator.EX);
break;
case LogicOperator.EX:
res = new FormulaNode(LogicOperator.AX);
break;
case LogicOperator.EU:
res = new FormulaNode(LogicOperator.AR);
break;
case LogicOperator.AU:
res = new FormulaNode(LogicOperator.ER);
break;
case LogicOperator.ER:
res = new FormulaNode(LogicOperator.AU);
break;
case LogicOperator.AR:
res = new FormulaNode(LogicOperator.EU);
break;
case LogicOperator.VAR:
res = new FormulaNode(LogicOperator.NOT);
res.SetChildren(new FormulaNode(this.childNodes[0].name), null);
return(res);
default:
res = null;
break;
}
if (this.childNodes[0].childNodes[0] != null)
{
left = new FormulaNode(LogicOperator.NOT);
left.SetChildren(this.childNodes[0].childNodes[0].NNF(), null);
left = left.NNF();
}
if (this.childNodes[0].childNodes[1] != null)
{
right = new FormulaNode(LogicOperator.NOT);
right.SetChildren(this.childNodes[0].childNodes[1].NNF(), null);
right = right.NNF();
}
res.SetChildren(left, right);
return(res);
}
private static FormulaNode Parse(List <Token> tokens)
{
FormulaNode result = null;
List <Token> rightSide = new List <Token>();
BinaryToken lastOp = null;
// the input is a single token - must be an atom or an unparsed string
if (tokens.Count == 1)
{
var tok = tokens[0] as LiteralToken;
if (tok.type == TokenType.ATOM)
{
return(new FormulaNode(tok.value));
}
return(Parse(ToplevelTokenize(tok.value)));
}
int minPrecedence = MAX_PRECEDENCE;
for (int i = 0; i < tokens.Count; i++)
{
if (tokens[i] is BinaryToken)
{
var op = tokens[i] as BinaryToken;
minPrecedence = Math.Min(minPrecedence, op.precedence);
}
}
if (minPrecedence == MAX_PRECEDENCE)
{
// the input didn't contain any toplevel binary operators
var opToken = tokens[0] as UnaryToken;
result = new FormulaNode(opToken.logicOperator);
var operand = Parse(tokens.GetRange(1, tokens.Count - 1));
if (untilOperators.Contains(opToken.logicOperator))
{
result.SetChildren(operand[0], operand[1]);
}
else if (quanitifers.Contains(opToken.logicOperator))
{
result.SetName(operand[0].GetName());
result.SetChildren(operand[1], null);
}
else
{
result.SetChildren(operand, null);
}
return(result);
}
// if we got here - split by lowest-precedence binary operator
foreach (Token t in tokens)
{
if (t is BinaryToken)
{
var op = t as BinaryToken;
if (op.precedence == minPrecedence)
{
if (result == null)
{
result = Parse(rightSide);
}
else
{
var leftSide = result;
result = new FormulaNode(lastOp.logicOperator);
result.SetChildren(leftSide, Parse(rightSide));
}
rightSide = new List <Token>();
lastOp = op;
continue;
}
}
rightSide.Add(t);
}
if (rightSide.Count != 0)
{
var leftSide = result;
result = new FormulaNode(lastOp.logicOperator);
result.SetChildren(leftSide, Parse(rightSide));
}
return(result);
}
