anchor.diff:            do (import nixpkgs {
               inherit system;
               config.allowUnfree = true;
  -            overlays = [ self.overlay ];
  +            overlays = lib.attrValues self.overlays;
             }));
   
         # Which python3 packages should be modified by the overlay?
  
positive.code:               pkgs.python3.pkgs.sphinx
                pkgs.yamllint
              ];
          });
      };
  }
  
negative.code:       pythonAttrs = lib.filterAttrs (name: _: isPython name);
  
      in {
        overlays.default = final: prev:
          {
            bifrost = final.callPackage bifrost { };
            bifrost-doc = final.callPackage bifrost-doc { };
  