{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs?rev=20fc948445a6c22d4e8d5178e9a6bc6e1f5417c8";
    nixpkgs-empyrean.url = "github:NixOS/nixpkgs?rev=2ebb6c1e5ae402ba35cca5eec58385e5f1adea04";
  };

  outputs = { self, nixpkgs, nixpkgs-empyrean }: {
    nixosConfigurations.catacomb = nixpkgs.lib.nixosSystem {
      system = "aarch64-linux";
      modules = [ ./machine/catacomb ];
    };
    nixosConfigurations.empyrean = nixpkgs-empyrean.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [ ./machine/empyrean ];
    };
  };
}