anchor.diff:          ((and (bignump number)
                 (bignump divisor))
            (%%bignum-truncate number divisor))
  -        (t (error "Argument combination not supported."))))
  +        (t (check-type number number)
  +           (check-type divisor number)
  +           (error "Argument combination not supported."))))
   
   (defun generic-rem (number divisor)
     (multiple-value-bind (quot rem)
  
positive.code:     rem))
  
  (defun generic-+ (x y)
    (error "TODO"))
  
  (define-lap-function %%bignum-- ()
    ;; Save on the lisp stack.
  
negative.code:         ((and (bignump x)
                (bignump y))
           (%%bignum-* x y))
          (t (check-type x number)
             (check-type y number)
             (error "Argument combination not supported."))))
  