anchor.diff:    nativeBuildInputs = [ cmake ];
   
     meta = with lib; {
  +    homepage = "https://eigen.tuxfamily.org";
       description = "C++ template library for linear algebra: vectors, matrices, and related algorithms";
       license = licenses.lgpl3Plus;
  -    homepage = "https://eigen.tuxfamily.org";
  +    maintainers = with maintainers; [ sander raskin ];
       platforms = platforms.unix;
  -    maintainers = with lib.maintainers; [ sander raskin ];
  -    inherit version;
     };
   }
  
positive.code: { lib, stdenv, fetchFromGitLab, cmake }:
  
  stdenv.mkDerivation rec {
    pname = "eigen";
  
negative.code: 
    src = fetchFromGitLab {
      owner = "libeigen";
      repo = pname;
      rev = version;
      hash = "sha256-oXJ4V5rakL9EPtQF0Geptl0HMR8700FdSrOB09DbbMQ=";
    };
  
    patches = [
  