anchor.diff:  
     # perl is only needed for patchShebangs fixup.
     buildInputs = [
  -    gmp mpfr pari ntl gsl blas mpfi
  -    readline gettext libpng libao perl
  +    gmp mpfr pari ntl gsl blas mpfi glpk
  +    readline gettext libpng libao perl ecm
       # gfortran.cc default output contains static libraries compiled without -fPIC
       # we want libgfortran.so.3 instead
       (stdenv.lib.getLib gfortran.cc)
  
positive.code: { stdenv, fetchurl, fetchpatch, texlive, bison, flex, liblapack
  , gmp, mpfr, pari, ntl, gsl, blas, mpfi
  , readline, gettext, libpng, libao, gfortran, perl
  , enableGUI ? false, libGLU_combined ? null, xorg ? null, fltk ? null
  }:
  
negative.code:   configureFlags = [
      "--enable-gc" "--enable-png" "--enable-gsl" "--enable-lapack"
      "--enable-pari" "--enable-ntl" "--enable-gmpxx" # "--enable-cocoa"
      "--enable-ao" "--enable-ecm" "--enable-glpk"
    ] ++ stdenv.lib.optionals enableGUI [
      "--enable-gui" "--with-x"
    ];
  