This example in the Rationale section:

  (define (foo x a b)
    (case
     ((plus) (+ a b))
     ((minus) (- a b))
     (else (assume #f "valid operators are plus/minus" x))))

has a missing <key> (after the "(case").

It should presumably be:

  (define (foo x a b)
    (case x
     ((plus) (+ a b))
     ((minus) (- a b))
     (else (assume #f "valid operators are plus/minus" x))))
--
	--Per Bothner
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