anchor.diff:  
           in { inherit (pkgs) bifrost-doc; } // cgens // bfs // pys);
   
  -      devShell = eachSystem (pkgs:
  -        let
  +      devShells = eachSystem (pkgs: {
  +        default = let
             pre-commit = pre-commit-hooks.lib.${pkgs.system}.run {
               src = ./.;
               hooks.nixfmt.enable = true;
  
positive.code:               pkgs.python3.pkgs.sphinx
                pkgs.yamllint
              ];
          });
      };
  }
  
negative.code:           do (import nixpkgs {
              inherit system;
              config.allowUnfree = true;
              overlays = lib.attrValues self.overlays;
            }));
  
        # Which python3 packages should be modified by the overlay?
  