(define bieber (list #\B #\i #\e #\b #\e #\r))

(define (starts-with-bieber? lst-chars)
  (starts-with-bieber?-chooser lst-chars bieber))

(define (starts-with-bieber?-chooser lst-chars bieber)
  (cond
    [(empty? lst-chars) false]
    [(empty? bieber) true]
    [else (and (char=? (first lst-chars) (first bieber))
          (starts-with-bieber?-chooser (rest lst-chars) (rest bieber)))]))