anchor.diff:  }:
   
   let
  -  version = "2020.1.2";
  +  version = "2020.3.4";
     shortVersion = builtins.substring 0 6 version;
     data = stdenv.mkDerivation rec {
       pname = "flightgear-data";
  
positive.code: 
      src = fetchurl {
        url = "mirror://sourceforge/flightgear/release-${shortVersion}/FlightGear-${version}-data.tar.bz2";
        sha256 = "0ldsjb54k8nb99h6n4f4x20nawd2pa0a8skkwkrgckdpmdv0zwyk";
      };
  
      phases = [ "installPhase" ];
  
negative.code: 
    src = fetchurl {
      url = "mirror://sourceforge/flightgear/release-${shortVersion}/${pname}-${version}.tar.bz2";
      sha256 = "02d9h10p8hyn0a25csragj6pbwmrir1z8zb92023s9vi21j7bwy8";
    };
  
    # Of all the files in the source and data archives, there doesn't seem to be
  