{self, ...}: {
  flake.overlays.crossover = final: prev: {
    crossover = final.callPackage ./_derivation.nix {};
  };
  flake.nixosModules.crossover-overlay = {
    nixpkgs.overlays = [self.overlays.crossover];
  };
  perSystem = {pkgs, ...}: {
    packages.crossover = pkgs.callPackage ./_derivation.nix {};
  };
}