Let-Over-Lambda book

is pretty lame.

http://letoverlambda.com/index.cl/guest/chap2.html

(defun block-scanner (trigger-string)
  (let* ((trig (coerce trigger-string 'list))
         (curr trig))
    (lambda (data-string)
      (let ((data (coerce data-string 'list)))
        (dolist (c data)
          (if curr
            (setq curr
                  (if (char= (car curr) c)
                    (cdr curr) ; next char
                    trig))))   ; start over
        (not curr))))) ; return t if found
"Here is a demonstration of its use, pretending to be some sort of communications tap watching out for a specific black-listed word, jihad:"

(defvar scanner (block-scanner "jihad")) ; SCANNER
(funcall scanner "We will start ")       ; NIL
(funcall scanner "the ji")               ; NIL
(funcall scanner "had tomorrow.")        ; T
but it fails already on:

(defparameter scanner (block-scanner "kkke")) ; SCANNER
(funcall scanner "kkkke")                     ; NIL

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now...

http://letoverlambda.com/index.cl/guest/chap5.html

(defun cxr-calculator (n)
  (loop for i from 1 to n
        sum (expt 2 i)))
but this can be done with simple arithmetics!

2^(n+1)-2