TIL about the ash function. So, (defun square (n) (ash 1 (1- n))) is way simpler compared to:

(defun power (n m)
  (reduce #'* (loop for x below n collect m)))

(defun square (n)
  (power (- n 1) 2))

(Me playing with the CL track at https://exercism.io). #lisp