This is a hypertext English translation of René Guitart’s paper Relations et carrés exacts (Guitart, 1980).

This version of the original text should be understood as a tribute to the author, as a way of making his paper more accessible to those who want to read it and do not know French well enough, as an excuse to understand its content myself, while making it clearer when needed (there are a few more words of explanation around definitions and theorems, and more diagrams/pictures wherever I felt it would have helped the reader).

All typos and mistakes that might result from this light editing come from my poor understanding and should not be attributed to the original author.