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(if (= major-length 4800) 18
  (if (= major-length 8552) (if (= val 4) 33
                              (if (= val 1) 18
                                (error "not handled")))
    (error "not handled")))

(cond ((= major-length 4800) 18)
      ((= major-length 8552) (cond ((= val 4) 33)
                                   ((= val 1) 18)
                                   (error "not handled")))
      (error "not handled"))

(ecase major-length
  (4800 18)
  (8552 (ecase var
          (4 33)
          (1 18))))