anchor.diff:  let 
     fetchurl = a.fetchurl;
   
  -  version = a.lib.attrByPath ["version"] "1.0.30" a; 
  +  version = a.lib.attrByPath ["version"] "1.0.29" a; 
     buildInputs = with a; [
       clisp makeWrapper
     ];
  
positive.code:   };
  }
  
  
negative.code: rec {
    src = fetchurl {
      url = "http://prdownloads.sourceforge.net/sbcl/sbcl-${version}-source.tar.bz2";
      sha256 = "1bdsn4rnrz289068f1bdnxyijs4r02if4p87fv726glp5wm20q1z";
    };
  
    inherit buildInputs;
  