anchor.diff:      lib.optionalAttrs (crossSystem == null && pkgs.stdenv ? overrides)
         (pkgs.stdenv.overrides pkgs);
   
  -  # The un-overriden packages, passed to `overrider'.
  -  pkgsInit = pkgsFun pkgs;
  -
     # Return the complete set of packages, after applying the overrides
     # returned by the `overrider' function (see above).  Warning: this
     # function is very expensive!
  -  applyGlobalOverrides = pkgsOrig: overrider:
  +  applyGlobalOverrides = overrider:
       let
         overrides = overrider pkgs pkgsOrig // stdenvOverrides pkgsOrig;
  +
  +      # The un-overriden packages, passed to `overrider'.
  +      pkgsOrig = pkgsFun pkgs;
   
         # The overriden, final packages.
         pkgs = pkgsFun pkgs // overrides;
  
positive.code:   #
    # The result is `pkgs' where all the derivations depending on `foo'
    # will use the new version.
    overridePackages = f: applyGlobalOverrides pkgs f;
  
    # Override system. This is useful to build i686 packages on x86_64-linux.
    forceSystem = system: kernel: (import ./../..) {
  
negative.code:   # (un-overriden) set of packages, allowing packageOverrides
    # attributes to refer to the original attributes (e.g. "foo =
    # ... pkgs.foo ...").
    pkgs = applyGlobalOverrides (self: config.packageOverrides or (super: {}));
  
    # stdenvOverrides is used to avoid circular dependencies for building the
    # standard build environment. This mechanism use the override mechanism to
  