TR issue with the type of expt

The following snippet:

--------------------------
#lang typed/racket
(: ** [Real Real -> Real])
(define (** a b)
  (expt a b))
--------------------------

Throws:
unsaved editor:5:2: Type Checker: type mismatch expected: Real given: Number in: (expt a b)
  #(67 10)


I believe (because I can’t think of a counterexample) that
(expt Real Real) is never Complex; and therefore expt can be of type
(Real Real -> Real).

First off, is the statement above true?

Is there a technical reason why my example HAS TO fall back to
(Number Number -> Number)? Or is this simply an oversight?

Regards,

Tim

Version: 6.6.0.4--2016-09-08(-/f) [3m].

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Tim Brown CEng MBCS <[email protected]>
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