# File lib/rgl/implicit.rb, line 126
126:     def vertices_filtered_by (&filter)
127:       implicit_graph { |g|
128:         g.vertex_iterator { |b|
129:           self.each_vertex { |v| b.call(v) if filter.call(v) }
130:         }
131:         g.adjacent_iterator { |v, b|
132:           self.each_adjacent(v) { |u| b.call(u) if filter.call(u) }
133:         }
134:       }
135:     end