these 2 derivations will be built:
  /nix/store/y0sq57v5aydvahj9qxarrv8jyrs0888h-xfractint-20.04p16.tar.gz.drv
  /nix/store/39n35ygkabsfck512n7q5j9dzm24k4fr-xfractint-20.04p16.drv