anchor.diff:  
   let
     inherit (lib) optional;
  -  version = "1.0";
  +  version = "1.2.1";
   in
   stdenv.mkDerivation {
     pname = "ripser";
  
positive.code: { lib, stdenv, fetchurl, fetchFromGitHub
  , assembleReductionMatrix ? false
  , useCoefficients ? false
  , indicateProgress ? false
  , useGoogleHashmap ? false, sparsehash ? null
  
negative.code:   src = fetchFromGitHub {
      owner = "Ripser";
      repo = "ripser";
      rev = "v${version}";
      sha256 = "sha256-BxmkPQ/nl5cF+xwQMTjXnLgkLgdmT/39y7Kzl2wDfpE=";
    };
  
    buildInputs = optional useGoogleHashmap sparsehash;
  
    buildFlags = [
      "-std=c++11"
      "-O3"
      "-D NDEBUG"
    ]
    ++ optional useCoefficients "-D USE_COEFFICIENTS"
    ++ optional indicateProgress "-D INDICATE_PROGRESS"
    ++ optional useGoogleHashmap "-D USE_GOOGLE_HASHMAP"
  