anchor.diff:  { stdenv, fetchurl, makeDesktopItem
   , python3, python3Packages
  -, glew, freeglut, libpng, libxml2, tk, freetype }:
  +, glew, freeglut, libpng, libxml2, tk, freetype, libmsgpack }:
   
   
   with stdenv.lib;
   
   let
     pname = "pymol";
  -  ver_maj = "1.8";
  -  ver_min = "4";
  +  ver_maj = "2";
  +  ver_min = "1";
     version = "${ver_maj}.${ver_min}.0";
     description = "A Python-enhanced molecular graphics tool";
   
  
positive.code:     name = "${pname}";
      exec = "${pname}";
      desktopName = "PyMol Molecular Graphics System";
      genericName = "Molecular Modeller";
      comment = description;
      mimeType = "chemical/x-pdb;chemical/x-mdl-molfile;chemical/x-mol2;chemical/seq-aa-fasta;chemical/seq-na-fasta;chemical/x-xyz;chemical/x-mdl-sdf;";
      categories = "Graphics;Education;Science;Chemistry;";
  
negative.code:   name = "pymol-${version}";
    src = fetchurl {
      url = "mirror://sourceforge/project/pymol/pymol/${ver_maj}/pymol-v${version}.tar.bz2";
      sha256 = "1qpacd5w4r9a0nm5iqmkd92ym3ai00dp7v61cwd6jgakk6wfps3s";
    };
  
    buildInputs = [ python3Packages.numpy glew freeglut libpng libxml2 tk freetype libmsgpack ];
    NIX_CFLAGS_COMPILE = "-I ${libxml2.dev}/include/libxml2";
  
    installPhase = ''
  