nx::Class create GraphPrinted -superclass Graph {
    :public method dot_print {} {
        append collections "graph {\n"
        foreach edge ${:edges} {
            append collections "\t"
            append collections "[string trim [$edge getN1] "::nsf::__#"] -- [string trim [$edge getN2] "::nsf::__#"]"
            append collections "\n"
        }
        append collections "}"
        puts $collections
        return $collections
    }
  }