{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }: flake-utils.lib.eachDefaultSystem (system:
    let
      pkgs = import nixpkgs { inherit system; };
      mkNocheck = drv: drv.overrideAttrs (o: {
        doCheck = false;
        checkInputs = [ ];
      });
    in
    {
      packages = rec {
        u01 = pkgs.callPackage
          ({ stdenv, catch2_3, cmake }: stdenv.mkDerivation {
            name = "ecg-u01";

            src = ./u01;

            nativeBuildInputs = [ cmake ];
            checkInputs = [ catch2_3 ];

            doCheck = true;
          })
          { };

        u02 = pkgs.callPackage
          ({ stdenv, catch2_3, cmake, freeglut, libGL, libGLU }: stdenv.mkDerivation {
            name = "ecg-u02";

            src = ./u02;

            nativeBuildInputs = [ cmake ];
            buildInputs = [ freeglut libGL libGLU ];
            checkInputs = [ catch2_3 ];

            doCheck = true;
          })
          { };

        u03 = pkgs.callPackage
          ({ stdenv, cmake, freeglut, libGL, libGLU }: stdenv.mkDerivation {
            name = "ecg-u03";

            src = ./u03;

            nativeBuildInputs = [ cmake ];
            buildInputs = [ freeglut libGL libGLU ];
          })
          { };

        u01-nocheck = mkNocheck u01;
        u02-nocheck = mkNocheck u02;
      };

      devShells.default = pkgs.mkShell {
        nativeBuildInputs = with pkgs; [ catch2_3 cmake freeglut libGL libGLU reuse ];
      };
    });
}