anchor.diff:      sha256 = "05736hamjv4f38jw6z9y4wckc7mz18ivbizm1s3pb0n6fp1sy4zk";
     };
   
  -  patches = [
  +  patches = lib.optionals withGraphviz [
       (substituteAll {
         src = ./graphviz.patch;
         inherit graphviz;
  
positive.code:     six
    ];
  
    # Fontconfig error: Cannot load default config file
    preCheck = ''
      export FONTCONFIG_FILE=${fontconfig.out}/etc/fonts/fonts.conf
    '';
  
    checkPhase = ''
      runHook preCheck
  
negative.code: , fetchpatch
  , nose
  , six
  , withGraphviz ? true
  , graphviz
  , fontconfig
  }:
  