public static SequentFormula Apply(SequentFormula first, SequentFormula second)
{
if (first.Consequent == null || second.Consequent == null)
{
return(null);
}
if (Implication.GetInstance().Equals(first.Consequent.TopConnective) == false)
{
return(null);
}
if (first.Consequent.GetOperand(0).Equals(second.Consequent) == false)
{
return(null);
}
var newAntecedents = new HashSet <Formula>();
foreach (var antecedent in first)
{
newAntecedents.Add(antecedent);
}
foreach (var antecedent in second)
{
newAntecedents.Add(antecedent);
}
var newConsequent = second.Consequent;
return(new SequentFormula(newAntecedents, newConsequent));
}
private static Symbol SpecialSymbol(string str, ref int index)
{
++index;
if (index >= str.Length)
{
throw new ArgumentException(
$"a tag was expected, but there is no tag before the symbol \\ with the number {index - 1}");
}
var tag = GetTag(str, ref index);
if (tag.Length == 0)
{
throw new ArgumentException(
$"a tag was expected, but there is no tag before the symbol \\ with the number {index - 1}");
}
return(tag switch
{
"lnot" => Negation.GetInstance(),
"lor" => Disjunction.GetInstance(),
"land" => Conjunction.GetInstance(),
"to" => Implication.GetInstance(),
"forall" => UniversalQuantifier.GetInstance(),
"exists" => ExistentialQuantifier.GetInstance(),
"over" => Division.GetInstance(),
"func" => GetFunction(str, ref index), // \func{name arity}
"pr" => GetPredicate(str, ref index), // \pr{name arity}
_ => throw new ArgumentException($"unknown tag {tag} before the symbol with the number {index}")
});