anchor.diff:  
     gnuplot = callPackage ../tools/graphics/gnuplot {
       inherit (gtkLibs) pango;
  -    wxGTK = if stdenv.isLinux then wxGTK else wxGTK.override { withMesa = false; };
       texLive = null;
       lua = null;
     };
  
positive.code: 
    maxima = callPackage ../applications/science/math/maxima { };
  
    wxmaxima = callPackage ../applications/science/math/wxmaxima {
      wxGTK = if stdenv.isLinux then wxGTK else wxGTK.override { withMesa = false; };
    };
  
    pari = callPackage ../applications/science/math/pari {};
  
  
negative.code:     inherit (gtkLibs) gtk;
      inherit (gst_all) gstreamer gstPluginsBase;
      inherit (gnome) GConf;
      withMesa = stdenv.isLinux;
    };
  
    wxGTK290 = callPackage ../development/libraries/wxGTK-2.9/2.9.0.nix {
  