+ ;; A real raised to a non-integral power can be a float or a
+ ;; complex number.
+ ((or (csubtypep x (specifier-type '(rational 0)))
+ (csubtypep x (specifier-type '(float (0d0)))))
+ ;; But a positive real to any power is well-defined.
+ (merged-interval-expt x y))
+ ((and (csubtypep x (specifier-type 'rational))
+ (csubtypep x (specifier-type 'rational)))
+ ;; A rational to the power of a rational could be a rational
+ ;; or a possibly-complex single float
+ (specifier-type '(or rational single-float (complex single-float))))