anchor.diff:      };
       
       installer = {
  -      nixpkgsURL = http://nix.cs.uu.nl/dist/nix/ + nixpkgsRel;
  +      nixpkgsURL = http://nixos.org/releases/nixpkgs/ + nixpkgsRel;
       };
   
       security = {
  
positive.code: rec {
  
    
    nixpkgsRel = "nixpkgs-0.12pre10553";
  
  
    configuration = {
  
negative.code: 
    # Get a recent copy of Nixpkgs.
    nixpkgsTarball = pkgs.fetchurl {
      url = configuration.installer.nixpkgsURL + "/nixexprs.tar.bz2";
      sha256 = "af5983ce0ac4bb5ad7786905d20fe4ae6bd4c43f6c831baa42bf15f09535dba4";
    };
  
  
  