if (ptgs[i] instanceof NamePtg) { continue; }
if (ptgs[i] instanceof NameXPtg) { continue; }
if (ptgs[i] instanceof UnknownPtg) { continue; }
if (ptgs[i] instanceof OperationPtg) {
OperationPtg optg = (OperationPtg) ptgs[i];
// parens can be ignored since we have RPN tokens
if (optg instanceof ParenthesisPtg) { continue; }
if (optg instanceof AttrPtg) { continue; }
if (optg instanceof UnionPtg) { continue; }