#racket

(define occurs-free?
  (lambda (var exp)
    (cond [(symbol? exp) (eqv? var exp)]
	  [(eqv? (car exp) 'lambda)
	   (and (not (eqv? (caadr exp) var))
		(occurs-free? var (caddr exp)))]
	  [else (or (occurs-free? var (car exp))
		    (occurs-free? var (cadr exp)))])))


(define occurs-bound?
  (lambda (var exp)
    (cond [(symbol? exp) #f]
	  [(eqv? (car exp) 'lambda)
	   (or (occurs-bound? var (caddr exp))
	       (and (eqv? (caadr exp) var)
		    (occurs-free? var (caddr exp))))]
	  [else (or (occurs-bound? var (car exp))
		    (occurs-bound? var (cadr exp)))])))