Queue is a circular queue of fixed length s is the oldest element in the queue or -1 if there are no elements t is the newest element in the queue or -1 if there are no elements a is a slice of fixed length that will hold the elements of the queue but those elements can only be read considering s and t Internal implementation: we will always have t greater or equal to s, considering they are on a circle with the pozitive sens from west ( 0 ) to est ( capacity ).