Num.diff

--- src/core/Num.pm.orig        2011-08-25 18:24:42.000000000 +0000
+++ src/core/Num.pm     2011-08-26 09:37:08.000000000 +0000
@@ -30,6 +30,7 @@ my class Num {
         while $r != 0 && abs($num - ($b/$d)) > $epsilon {
             ($r, $q) = modf(1/$r);
 
+            die("Provided Num does not fit into a Rat\n") if $a < 0 || $b < 0;
             ($a, $b) = ($b, $q*$b + $a);
             ($c, $d) = ($d, $q*$d + $c);
         }