Commentary on the First Book of Euclid's Elements

...knowledge of all literature, not sent me the most excellent Munich codex. From this, I began to hope that I could produce an edition—if not perfect and absolute in every part—at least one much more corrected and less incomplete, and therefore pleasing to many learned men. Whatever time, therefore, was free from the duties of public office and other responsibilities, I spent on the commentaries of Proclus, and the fruit of my labor now appears in print.

Which books I used in completing the work is evident from the explanation of the notes, which precedes the words of Proclus below. In this place, a few things must be added both about the manuscript codices and about the form of the text.

All the codices we know of, in which the commentaries of Proclus are read, are derived from one and the same exemplar; this is a very certain document because of the lacunae gaps in the text that consumed the end of the commentary on the 36th proposition of Euclid along with the beginning of the next, and the end of the commentary on the 41st along with the commentary on the 42nd and the beginning of the commentary on the 43rd. Variations of words and sentences also reveal such a kinship to a great extent, born from the various remedies of scribes or correctors for the same defect. For there were not lacking those who read those commentaries. There are also very clear traces that the Munich codex was revised by an inexpert hand, but it is very difficult to judge whether the same person who wrote the codex also corrected it, or whether someone else checked it not long after. In many places, the hand of the corrector barely differs from the hand of the writer; in other places, paler ink and brushstrokes of letters that are either more negligent or more recent seem to reveal a later hand. One may therefore conjecture that several readers worked on this manuscript, to whom one can no longer assign their own specific contributions; I am, however, persuaded that at least one of them, if not more, was a learned man who, shortly after the codex was written, saw and corrected some of its errors.