The Praefatio is a Latin translation of Ramus' Préface sur le proëme des mathémathiques. Books I-III constitute the author's Proemium mathematicum (first published in Paris in 1567). Books IV-V are Ramus' commentary on his own Arithmetices. Books VI-XXXI constitute his commentary on Euclid's Elements--Cf. Ong, W.J. Ramus and Talon inventory, p. 438.