public override Object visitNotSentence(UnarySentence ns, Object arg)
{
List<Symbol> s = (List<Symbol>)arg;
if (ns.getNegated() is Symbol)
{
// do nothing .do NOT add a negated Symbol
}
else
{
s = SetOps
.union(s, (List<Symbol>)ns.getNegated().accept(this, arg));
}
return s;
}