// expr is changed in place, so that it does not contain synonims
final int position = _nt.indexOf(_inputTupleSchema, expr);
if (position != ParserUtil.NOT_FOUND) {
// we found an expression already in the tuple schema
final TypeConversion tc = _nt.getType(_inputTupleSchema, expr);
final ValueExpression ve = new ColumnReference(tc, position,
ParserUtil.getStringExpr(expr));
pushToExprStack(ve);
return true;
} else
return false;