The user receives the task assigned on the basis of one of the 5 predefined levels
or a previously prepared custom level. E.g. Answer "Y" if you see two different
shapes, answer "N" otherwise.
When two shapes appear on semaphores C and D the user selects one of the two
answers; a different sound distinguishes the right answer from the wrong one. If
the user does not answer in the allotted time (1 second at the beginning) the
answer is considered as if it were wrong and consequently at the next turn the
available number of milliseconds is increased. On the contrary, the more right
answers are given the more the time shortens, making the exercise harder