Long description

Figure a: It contains a square block labeled R pointed vertically upward to a circle labeled A.

Figure b: It contains a circle labeled B pointed vertically upward to a square block labeled S.

Figure c: Here the circle labeled D points toward a block labeled U. The block U points toward a circle labeled C. Again an arrow from C points to a block labeled T. The T block points back to circle D. This forms a circular path.