anchor.diff:    buildInputs = [ cmake
                     netcdf
                     gfortran
  -                  jasper
                     libpng
  +                  openjpeg
                   ] ++ stdenv.lib.optionals enablePython [
                     pythonPackages.python
                   ];
  
positive.code:   cmakeFlags = [ "-DENABLE_PYTHON=${if enablePython then "ON" else "OFF"}"
                   "-DENABLE_PNG=ON"
                   "-DENABLE_FORTRAN=ON"
                 ];
  
    enableParallelBuilding = true;
  
negative.code: { fetchurl, fetchpatch, stdenv,
    cmake, netcdf, gfortran, libpng, openjpeg,
    enablePython ? false, pythonPackages }:
  
  stdenv.mkDerivation rec{
  