// The stack contains either ... TS, Filter or
// ... TS, Filter, Filter with the head of the stack being the rightmost
// symbol. So we just pop out the two elements from the top and if the
// second one of them is not a table scan then the operator on the top of
// the stack is the Table scan operator.
Node tmp = stack.pop();
Node tmp2 = stack.pop();
TableScanOperator top = null;
Operator<? extends Serializable> pop = null;
if (tmp2 instanceof TableScanOperator) {
top = (TableScanOperator) tmp2;
pop = top;