anchor.diff:  { stdenv
   , fetchFromGitHub
   , cairo
  -, imagemagick
  +, graphicsmagick
   , pkg-config
   , pngquant
   , python3
   , which
   , zopfli
  +, fetchpatch
   }:
   
   let
  
positive.code: 
    nativeBuildInputs = [
      cairo
      imagemagick
      pkg-config
      pngquant
      python
      which
      zopfli
    ];
  
    postPatch = let
  
negative.code:     ## Non-artwork is MIT
      license = with licenses; [ asl20 ofl cc-by-40 mit ];
      maintainers = with maintainers; [ jtojnar ];
    };
  }
  