Which of the functions are continuous, which are discontinuous? The fields at the bottom may be moved by mouse dragging - try to associate them with the expressions given. The "Reset" button restores the original situation, the fields being placed at random positions. Below the puzzle, you may activate an evaluation in terms of number of points achieved.

Below, sgn(x) denotes the sign function. It is defined by

          sgn(x) = 1 for x > 0
          sgn(x) = –1 for x < 0
          sgn(0) = 0