anchor.diff:    elan = callPackage ../applications/science/logic/elan {};
     mathlibtools = with python3Packages; toPythonApplication mathlibtools;
   
  -  leo2 = callPackage ../applications/science/logic/leo2 {
  -     ocaml = ocaml-ng.ocamlPackages_4_01_0.ocaml;};
  +  leo2 = callPackage ../applications/science/logic/leo2
  +    { ocaml = ocaml-ng.ocamlPackages_4_01_0.ocaml; };
   
     leo3-bin = callPackage ../applications/science/logic/leo3/binary.nix {};
   
  
positive.code: 
    nixops-dns = callPackage ../tools/package-management/nixops/nixops-dns.nix { };
  
    /* Evaluate a NixOS configuration using this evaluation of Nixpkgs.
  
       With this function you can write, for example, a package that
       depends on a custom virtual machine image.
  
       Parameter: A module, path or list of those that represent the
                  configuration of the NixOS system to be constructed.
  
       Result:    An attribute set containing packages produced by this
                  evaluation of NixOS, such as toplevel, kernel and
                  initialRamdisk.
                  The result can be extended in the modules by defining
                  extra attributes in system.build.
                  Alternatively, you may use the result's config and
                  options attributes to query any option.
  
       Example:
  
           let
             myOS = pkgs.nixos ({ lib, pkgs, config, ... }: {
  
               config.services.nginx = {
                 enable = true;
                 # ...
               };
  
               # Use config.system.build to exports relevant parts of a
               # configuration. The runner attribute should not be
               # considered a fully general replacement for systemd
               # functionality.
               config.system.build.run-nginx = config.systemd.services.nginx.runner;
             });
           in
             myOS.run-nginx
  
       Unlike in plain NixOS, the nixpkgs.config and
       nixpkgs.system options will be ignored by default. Instead,
       nixpkgs.pkgs will have the default value of pkgs as it was
       constructed right after invoking the nixpkgs function (e.g. the
       value of import <nixpkgs> { overlays = [./my-overlay.nix]; }
       but not the value of (import <nixpkgs> {} // { extra = ...; }).
  
       If you do want to use the config.nixpkgs options, you are
       probably better off by calling nixos/lib/eval-config.nix
       directly, even though it is possible to set config.nixpkgs.pkgs.
  
       For more information about writing NixOS modules, see
       https://nixos.org/nixos/manual/index.html#sec-writing-modules
  
       Note that you will need to have called Nixpkgs with the system
       parameter set to the right value for your deployment target.
    */
    nixos =
      configuration:
  
negative.code:   wallutils = callPackage ../tools/graphics/wallutils { };
  
    wrangler = callPackage ../development/tools/wrangler {
      inherit (darwin.apple_sdk.frameworks) CoreFoundation CoreServices Security;
    };
  
    wsl-open = callPackage ../tools/misc/wsl-open { };
  