anchor.diff:  let 
     fetchurl = a.fetchurl;
   
  -  version = a.lib.attrByPath ["version"] "3.4" a; 
  +  version = a.lib.attrByPath ["version"] "3.5" a; 
     buildInputs = with a; [
       aalib gsl libpng libX11 xproto libXext xextproto 
       libXt zlib gettext intltool perl
  
positive.code: in
  rec {
    src = fetchurl {
      url = "http://prdownloads.sourceforge.net/xaos/XaoS-${version}.tar.gz";
      sha256 = "004cdb0xv14shyixs79bf95s52s7aidr5bqfn9wb49gpasrsknrc";
    };
  
    inherit buildInputs;
  
negative.code:       
    name = "xaos-" + version;
    meta = {
      homepage = http://xaos.sourceforge.net/;
      description = "XaoS - fractal viewer";
      license = "GPLv2+";
    };
  }
  