anchor.diff:  rec {
   
     
  -  nixpkgsRel = "nixpkgs-0.12pre10553";
  +  nixpkgsRel = "nixpkgs-0.12pre11712-4lrp7j8x";
   
   
     configuration = {
  
positive.code: 
    # Get a recent copy of Nixpkgs.
    nixpkgsTarball = pkgs.fetchurl {
      url = configuration.installer.nixpkgsURL + "/" + nixpkgsRel + ".tar.bz2";
      md5 = "a6f1cd8486b7d588ecc7d98f5baf6a73";
    };
  
  
  
negative.code:     };
      
      installer = {
        nixpkgsURL = http://nixos.org/releases/nixpkgs/ + nixpkgsRel;
      };
  
      security = {
  