Welcome to the CHICKEN Scheme pasting service

(use utf8)

(define abc "abcdefghijklmnopqrstuvwxyz")
(define ɐqɔ "ɐqɔpəɟɓɥıɾʞʅɯuodbɹsʇnʌʍxʎz")

(define mapdɐɯ
  (map cons (string->list abc) (string->list ɐqɔ)))

(define (inv c) (or (alist-ref c mapdɐɯ) c))

(define (invert s)
  (list->string
   (reverse
    (map inv (string->list s)))))

(unless (null? (command-line-arguments))
  (print (invert (car (command-line-arguments)))))

#| easy mode:
(use utf8-srfi-13)
(define (invert s)
  (string-reverse (string-translate s abc ɐqɔ)))
|#