def rect_corners(rect):
    """ Returns cornerpoints of given rectangle.
    
        >>> rect_corners((1,2,1,3))
        ((1, 2), (2, 2), (2, 5), (1, 5))
    """
    tl = (rect[0],rect[1])
    tr = (rect[0]+rect[2],rect[1])
    br = (rect[0]+rect[2],rect[1]+rect[3])
    bl = (rect[0],rect[1]+rect[3])
    return (tl,tr,br,bl)