* [GRAPH_THEORY,NEW] Added adjacent_edges/3.
* [GRAPH_THEORY,SC] Renamed adjacent/3 to adjacent_vertices/3.
* [GRAPH_THEORY,NEW] Added degree/2.
* [GRAPH_THEORY,NEW] Added dominating_vertex/2.
* [GRAPH_THEORY,SC] Renamed edge/3 to edge_components/3.
* [GRAPH_THEORY,NEW] Added eddge/3.
* [GRAPH_THEORY,NEW] Implemented direct_subgraph/2.
* [SET_THEORY,NEW] Added direct_subset/2.