Unify NewGraph with a new graph obtained by deleting the list 
of
Vertices and all the edges that start from or go to a vertex 
in
Vertices to the Graph. Example:
?- del_vertices([1-[3,5],2-[4],3-[],4-[5],5-[],6-[],7-[2,6],8-[]],
                [2,1],
                NL).
NL = [3-[],4-[5],5-[],6-[],7-[6],8-[]]
- Compatibility
- Upto 5.6.48 the argument order was (+Vertices, +Graph, 
-NewGraph). Both YAP and SWI-Prolog have changed the argument 
order for compatibility with recent SICStus as well as consistency with del_edges/3.