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# Long description

The figure shows two parallel horiontal lines. The upper one is labelled q1 and the lower one is labelled q2. Near the left end of both lines are square boxes each containing a capital letter H. Further along the upper line is a large dot. A vertical line leads from this dot to the lower line where it joins a large circle with a large plus sign in it. Still further along the upper line is a large circle with a large plus sign in it. Even further along the upper line is another large circle with a large plus sign in it. A vertical line leads from this circle to the lower line where it joins a large dot. Near the right hand ends of both the upper and lower lines are square boxes each with a curved line and an arrow in it.