Complex sentence: Theon wrote several commentaries on the works of mathematicians and philosophers of the time; he authored three works on the philosophy of Plato, of which two are lost, and the only one which survives is "On Mathematics Useful for the Understanding of Plato".
Split into simpler sentences: Theon wrote several commentaries on the works of mathematicians and philosophers of the time; he authored three works on the philosophy of Plato, of which two are lost. The only one which survives is "On Mathematics Useful for the Understanding of Plato".