(define add1-to-all
  (lambda (ls)
    ; REQUIRES: atoms in ls are numbers
    (cond
     ((null? ls) '())
     ((pair? (car ls))
      (cons (add1-to-all (car ls))
	    (add1-to-all (cdr ls))))
     (else (cons (add1 (car ls))
		 (add1-to-all (cdr ls))))
     )))