(define (make-account balance password)
  
  (define (withdraw amount)
      (if (>= balance amount)
          (begin (set! balance (- balance amount))
                 balance)
          "Insufficient amount"))
    
  (define (deposit amount)
    (begin (set! balance (+ balance amount))
           balance))
  
  (define (dispatch m)
    (cond ((eq? m 'joint) set-password)
          ((eq? m 'withdraw) withdraw)
          ((eq? m 'deposit) deposit)
          (else 
           (error "Unknow request --- MAKE-ACCOUNT" m))))
  
  (define (set-password password)
    (define (validate psw op)
      (if (eq? psw password)
          (dispatch op)
          (error "Incorrect password")))
    validate)
  
  (set-password password))
    
    
(define (make-joint account origin-password new-password)
  ((account origin-password 'joint) new-password))
   

(define acc (make-account 100 'ssd))
(define acc-alias (make-joint acc 'ssd 'kk))

((acc 'ssd 'withdraw) 20)
((acc 'ssd 'withdraw) 30)

((acc-alias 'kk 'withdraw) 10)
((acc-alias 'kk 'deposit) 60)

((acc 'ssd 'withdraw) 0)