anchor.diff:  }:
   
   let
  -  inherit (nixpkgs) fetchpatch fetchurl symlinkJoin callPackage nodePackages_8_x;
  +  inherit (nixpkgs) fetchpatch fetchurl symlinkJoin callPackage nodePackages;
   
     # https://trac.sagemath.org/ticket/15980 for tracking of python3 support
     python = nixpkgs.python2.override {
  
positive.code:         inherit pythonEnv;
          inherit sage-src openblas-blas-pc openblas-cblas-pc openblas-lapack-pc pynac singular;
          pkg-config = nixpkgs.pkgconfig; # not to confuse with pythonPackages.pkgconfig
          three = nodePackages_8_x.three;
        };
  
        sage = self.callPackage ./sage.nix { };
  
negative.code:       env-locations = self.callPackage ./env-locations.nix {
          inherit pari_data ecl;
          inherit singular;
          three = nodePackages.three;
          mathjax = nodePackages.mathjax;
        };
  
        sage-env = self.callPackage ./sage-env.nix {
  