public bool IsClosed()
{
if (leftNode != null)
{
if (rightNode != null)
{
return(leftNode.IsClosed() && rightNode.IsClosed());
}
return(leftNode.IsClosed());
}
return(ExistsContradiction());
}
public ST(Node proposition)
{
Root = new STElement(new HashSet <Node> {
new NegationSign(proposition)
}, new List <char>(), "");
Root.Simplify();
IsTautology = Root.IsClosed();
}