checks if a given payload is in a root of the dag . concode_field_sep List<DirectedAcyclicGraphNode<T>> mRoots concode_elem_sep Map<T,DirectedAcyclicGraphNode<T>> mIndex concode_field_sep void add concode_elem_sep void deleteLeaf concode_elem_sep List<T> getParents concode_elem_sep List<T> sortTopologically concode_elem_sep List<T> getChildren concode_elem_sep boolean contains concode_elem_sep List<T> getRoots concode_elem_sep List<T> getAllInTopologicalOrder