anchor.diff: -{ stdenv, fetchurl, python2 }:
  +{ stdenv, fetchurl, python2, makeWrapper }:
   
   stdenv.mkDerivation rec {
     name = "lhapdf-${version}";
  
positive.code:     sha256 = "0bi02xcmq5as0wf0jn6i3hx0qy0hj61m02sbrbzd1gwjhpccwmvd";
    };
  
    buildInputs = [ python2 ];
  
    enableParallelBuilding = true;
  
negative.code:   passthru = {
      pdf_sets = import ./pdf_sets.nix { inherit stdenv fetchurl; };
    };
  
    postInstall = ''
      wrapProgram $out/bin/lhapdf --prefix PYTHONPATH : "$(toPythonPath "$out")"
    '';
  
    meta = {
      description = "A general purpose interpolator, used for evaluating Parton Distribution Functions from discretised data files";
  