anchor.diff:      VBmix = [ pkgs.gsl pkgs.fftw pkgs.qt4 ];
       WhopGenome = [ pkgs.zlib ];
       XBRL = [ pkgs.zlib pkgs.libxml2 ];
  +    xml2 = [ pkgs.libxml2 ];
       XML = [ pkgs.libtool pkgs.libxml2 pkgs.xmlsec pkgs.libxslt ];
     };
   
  
positive.code: 
    otherOverrides = old: new: {
      xml2 = old.xml2.overrideDerivation (attrs: {
        preConfigure = ''
          export LIBXML_INCDIR=${pkgs.libxml2}/include/libxml2
          export LIBXML_LIBDIR=${pkgs.libxml2}/lib
        '';
      });
  
      curl = old.curl.overrideDerivation (attrs: {
  
negative.code:     "WideLM" # depends on proprietary cudatoolkit
      "x_ent" # requires opencpu
      "xergm" # requires nlopt
      "ZeligMultilevel" # Requires Nlopt
      "zetadiv" # requires nlopt
      "zoib" # tarball is invalid on server
  