(define (new-account balance)

  (define (withdraw amount)
    (if (>= balance amount)
      (begin
        (set! balance (- balance amount)) 
        balance)
      (error "Insufficient funds") ) )

  (define (deposit amount)
    (set! balance (+ balance amount)) 
    balance)

  (define (respond-to-msg msg)
    (cond
      ((eq? msg 'withdraw) withdraw)
      ((eq? msg 'deposit) deposit)
      (else (error "Unknown operation")) ) )

  respond-to-msg)