[Updated the comment.
nad**20040616103801] hunk ./ChasingBottoms/IsBottom.hs 14
--- then @'isBottom' a = 'True'@.
+-- then @'isBottom' a = 'True'@. Other caught exceptions are
+-- re-thrown. If @a@ never reaches a weak head normal form and
+-- never throws an exception, then @'isBottom' a@ never terminates.