// and add the new union
List<OperatorIDTuple> succeddingsOfAll = this.join1
.getSucceedingOperators();
for (OperatorIDTuple _child : succeddingsOfAll) {
_child.getOperator().removePrecedingOperator(this.join1);
union_new.addSucceedingOperator(_child);
_child.getOperator().addPrecedingOperator(union_new);
}
// delete unreachable operators...
this.deleteOperatorWithoutParentsRecursive(this.join1, _startNodes);
this.deleteOperatorWithoutParentsRecursive(this.union1, _startNodes);