anchor.diff:    (:documentation "Represents an instance of a lesson, mostly for when a
                      lesson is given to parts of a class separately"))
   
  -(defmacro request-url (url &rest params)
  -  "Requests the URL using drakma, automatically supplying the cookie jar"
  -  `(drakma:http-request ,url
  -                        ,@params
  -                        :cookie-jar *cookie-jar*))
  -
   (defun timestamp->datestring (timestamp)
     "Converts a timestamp to a `datestring`"
     (local-time:format-timestring NIL timestamp :format '((:year 4) (:month 2) (:day 2))))
  
positive.code: (defun refresh-classes ()
    "sets *classes* to an alist of (classname . classid) pairs"
    (let ((json (st-json:read-json 
  	       (request-url *base-url*))))
      (setf *classes*
  	  (mapcar #'(lambda (item)
  		      (cons (st-json:getjso "name" item)
  
negative.code: (pushnew '("text" . "html") drakma:*text-content-types*)
  
  (defvar *classes*)
  
  (local-time:define-timezone 
      amsterdam 
  