return Collections.unmodifiableList(requiredTEs);
}
public void addOptionalTE(GraphPattern gp) {
List<ValueExpr> constraints = gp.removeAllConstraints();
TupleExpr tupleExpr = gp.buildTupleExpr();
OptionalTupleExpr optTE;
if (constraints.isEmpty()) {
optTE = new OptionalTupleExpr(tupleExpr);