sentences:  These three 2-way relations are not independent (i.e.both the synodic month and eclipse year are dependent on the apparent motion of the Sun, both the draconic month and eclipse year are dependent on the motion of the nodes), and indeed the eclipse year can be described as the beat period of the synodic and draconic months (i.e.the period of the difference between the synodic and draconic months); in formula