Three works in one pair of covers. The sutras are a set of mental pegs on which to hang the principles and precepts of a system which you must learn from a living teacher of your school. The bhasya of Vyasa is a reinvestiture of the skeleton of the sutras with the flesh and blood of comprehensible details. And the Tika of Vacaspati is of course a commentary on the Bhasya. The Bhasya is the oldest written systematic exposition of Yoga-doctrine in sanskrit that we posses.
When one considers the floods of pseudoscientific writing with which the propagandists of Indian "isms" have deluged people one is better prepared to appreciate the self-restraint of Dr. Woods in keeping all that pertains to miracle mongering and sencationalism in the background and in devoting himself to the exposition of the spiritual and intellectual aspects of Yoga.