### Semicolon style

The standard explains common semicolon comment style in section 2.4.4.2. Section 2.4.4.2.5 includes this short example showing typical use of one through four semicolons:

;;;; Math Utilities ;;; FIB computes the the Fibonacci function in the traditional ;;; recursive way. (defun fib (n) (check-type n integer) ;; At this point we're sure we have an integer argument. ;; Now we can get down to some serious computation. (cond ((< n 0) ;; Hey, this is just supposed to be a simple example. ;; Did you really expect me to handle the general case? (error "FIB got ~D as an argument." n)) ((< n 2) n) ;fib[0]=0 and fib[1]=1 ;; The cheap cases didn't work. ;; Nothing more to do but recurse. (t (+ (fib (- n 1)) ;The traditional formula (fib (- n 2)))))) ; is fib[n-1]+fib[n-2].