A.42 library(ugraphs): Unweighted Graphs
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Availability::- use_module(library(ugraphs)).(can be autoloaded)
Sourcedel_vertices(+Graph, +Vertices, -NewGraph)
Unify NewGraph with a new graph obtained by deleting the list of Vertices and all edges that start from or go to a vertex in Vertices from Graph. Example: 
?- del_vertices([2,1],
                [1-[3,5],2-[4],3-[],4-[5],
                 5-[],6-[],7-[2,6],8-[]],
                NL).
NL = [3-[],4-[5],5-[],6-[],7-[6],8-[]]