anchor.diff:    };
   
     passthru = {
  -    compatibleCoqVersions = v: builtins.elem v [ "8.6" "8.7" "8.8" "8.9" ];
  +    compatibleCoqVersions = v: builtins.hasAttr v coqVersions;
     };
   }
  
positive.code:     make -f Makefile.coq COQLIB=$out/lib/coq/${coq.coq-version}/ install
    '';
  
    meta = with stdenv.lib ; {
      homepage = http://color.inria.fr/;
      description = "CoLoR is a library of formal mathematical definitions and proofs of theorems on rewriting theory and termination whose correctness has been mechanically checked by the Coq proof assistant.";
      maintainers = with maintainers; [ jpas jwiegley ];
  
negative.code: { stdenv, fetchFromGitHub, coq, bignums }:
  
  let
    coqVersions = {
      "8.6" = "1.4.0";
      "8.7" = "1.4.0";
      "8.8" = "1.6.0";
      "8.9" = "1.6.0";
    };
    params = {
      "1.4.0" = {
        version = "1.4.0";
        rev = "168c6b86c7d3f87ee51791f795a8828b1521589a";
        sha256 = "1d2whsgs3kcg5wgampd6yaqagcpmzhgb6a0hp6qn4lbimck5dfmm";
      };
      "1.6.0" = {
        version = "1.6.0";
        rev = "328aa06270584b578edc0d2925e773cced4f14c8";
        sha256 = "07sy9kw1qlynsqy251adgi8b3hghrc9xxl2rid6c82mxfsp329sd";
      };
    };
    param = params.${coqVersions.${coq.coq-version}};
  in
  
  stdenv.mkDerivation {
    name = "coq${coq.coq-version}-CoLoR-${param.version}";
  
    src = fetchFromGitHub {
      owner = "fblanqui";
      repo = "color";
      inherit (param) rev sha256;
    };
  
    buildInputs = [ coq bignums ];
  