/// <summary>
/// Applies backwards the relevant operator effects and operator preconditions to the given target conditions.
/// </summary>
/// <param name="expression">Target conditions in CNF.</param>
/// <param name="expressionSubstitution">Variables substitution of the expression.</param>
/// <returns>Preceding conditions.</returns>
private ConditionsCNF ApplyBackwardsImpl(ConditionsCNF expression, ISubstitution expressionSubstitution)
{
UsedGroundedPredicates.Clear();
UsedGroundedFunctions.Clear();
ExpressionSubstitution = expressionSubstitution;
// remove positively contributing effects from the target conditions
ConditionsCNF resultExpression = ProcessPrimitiveEffects(expression);
resultExpression = ProcessForallEffects(resultExpression);
resultExpression = ProcessWhenEffects(resultExpression);
// unite processed conditions with partially grounded preconditions of the operator
if (OperatorPreconditions != null)
{
var preconditions = ClearRigidRelations(OperatorPreconditions);
resultExpression.Merge((ConditionsCNF)GroundConditions(preconditions).GetCNF());
}
return(resultExpression);
}
/// <summary>
/// Visits the expression.
/// </summary>
/// <param name="expression">Expression.</param>
public IElementCNF Visit(PredicateLiteralCNF expression)
{
var positivePredicateEffects = Effects.GroundedPositivePredicateEffects;
var negativePredicateEffects = Effects.GroundedNegativePredicateEffects;
if ((!expression.IsNegated && positivePredicateEffects.Count == 0) || (expression.IsNegated && negativePredicateEffects.Count == 0))
{
return(expression.Clone());
}
IAtom atom = GroundAtom(expression.PredicateAtom);
bool positivelyContributing = (expression.IsNegated) ? negativePredicateEffects.Contains(atom) : positivePredicateEffects.Contains(atom);
if (positivelyContributing)
{
UsedGroundedPredicates.Add(atom);
return(null);
}
return(expression.Clone());
}