anchor.diff:    # Get a recent copy of Nixpkgs.
     nixpkgsTarball = pkgs.fetchurl {
       url = configuration.installer.nixpkgsURL + "/" + nixpkgsRel + ".tar.bz2";
  -    md5 = "22deefec0696d2fb263864b97e2238d3";
  +    md5 = "a25cd6eb5e753703823fdd3ae86e9f25";
     };
   
   
  
positive.code: rec {
  
    
    nixpkgsRel = "nixpkgs-0.12pre9486";
  
  
    configuration = {
  
negative.code:     environment = {
        extraPackages = pkgs: [
          pkgs.vim
          pkgs.subversion # for nixos-checkout
        ];
      };
     
  