[plt-scheme] Some contract advice

Is the best way to write a contract for a function that takes a list
of natural numbers of length >= 2 and outputs a list of natural
numbers that is the same length as the input?

(->d
     ([argument (and/c (flat-named-contract
                        'arg-len->=2-required
                        (λ (ls) (>= (length ls) 2)))
                       (listof natural-number/c))])
     ()
     (result (and/c (flat-named-contract
                     'res-len-must-match-arg-len
                     (λ (ls) (= (length ls) (length argument))))
                    (listof natural-number/c))))