Calendar is a system for counting and grouping days that aims to primarily meet the marking of any task. In this case, calendars are useful for track homework assignments.
This is because, the calendar helps us to mark a time that the clock is no longer possible. He gives us a "direction" so that we do not get lost in the days that pass and we do not lose what we have to do each day.
It is usually referred to by using letters to indicate which lines rhyme; lines designated with the same letter all rhyme with each other. So it would be AA,BB
