dependencies in occurrence typing

gistfile1.txt

#lang typed/racket


(: foo (Any Any -> Number))
(define (foo x y)
  (cond
    [(or (and (string? x) (string? y))
         (and (number? x) (number? y)))
     (if (number? x)
         y ;; <- doesn't typecheck
         (string-length y))] ;; <- this does -- both should work
    [else 42]))