anchor.diff:  , hello
   }:
   
  -stdenv.mkDerivation rec {
  +stdenv.mkDerivation (self: {
     pname = "hello";
     version = "2.12";
   
     src = fetchurl {
  -    url = "mirror://gnu/hello/${pname}-${version}.tar.gz";
  +    url = "mirror://gnu/hello/${self.pname}-${self.version}.tar.gz";
       sha256 = "1ayhp9v4m4rdhjmnl2bq3cibrbqqkgjbl3s7yk2nhlh8vj3ay16g";
     };
   
  
positive.code: { lib
  , stdenv
  , fetchurl
  , nixos
  
negative.code:         (nixos { environment.noXlibs = true; }).pkgs.hello;
    };
  
    passthru.tests.run = runCommand "hello-test-run" {
      nativeBuildInputs = [ self ];
    } ''
      diff -U3 --color=auto <(hello) <(echo 'Hello, world!')
      touch $out
    '';
  
    meta = with lib; {
      description = "A program that produces a familiar, friendly greeting";
      longDescription = ''
  