anchor.diff:      readline
       ntl
       flint
  -  ] ++ stdenv.lib.optionals enableGfanlib [
  +  ] ++ lib.optionals enableGfanlib [
       cddlib
     ];
     nativeBuildInputs = [
  
positive.code: { stdenv, fetchurl, gmp, bison, perl, ncurses, readline, coreutils, pkgconfig
  , autoreconfHook
  , file
  , flint
  
negative.code:   # simple test to make sure singular starts and finds its libraries
    doInstallCheck = true;
    installCheckPhase = ''
      "$out/bin/Singular" -c 'LIB "freegb.lib"; exit;'
      if [ $? -ne 0 ]; then
          echo >&2 "Error loading the freegb library in Singular."
          exit 1
  