Fixed compare() mishap

domains/interval.ml

@@ -91,7 +91,7 @@ module Interval : NAKED_VALUE_DOMAIN = struct
           in
           let r2 =
             rand
-              (if Z.geq z1.lower z2.lower then Z.succ z2.lower else z1.lower)
+              (if Z.geq z1.lower z2.lower then Z.succ z1.lower else z2.lower)
               z2.upper
           in
           (r1, r2)