# File lib/rgl/base.rb, line 167
167:     def each_edge (&block)
168:       if directed?
169:         each_vertex { |u|
170:           each_adjacent(u) { |v| yield u,v }
171:         }
172:       else
173:         each_edge_aux(&block)       # concrete graphs should to this better
174:       end
175:     end