(define (assert x . rest)
  (define (assert-single x)
    (if (not (boolean? x)) (error "x is not boolean")
        (if (not x) (error "x is false"))))
  (define (assert-multi args)
    (assert-single (car args))
    (let ((rest (cdr args)))
      (if (not (nil? rest))
          (assert-multi rest))))
  (assert-multi (cons x rest)))