Dear @soulsistashakti, this is a very old book, the author was a professor from the The Salvador University in Buenos Aires, he was professor at the Oriental Studies Catedra in this University in Argentina. Here is very difficult to find it because the editorial are not printed it any more! but for me is a bible! sure you could find it in pdf mode but in spanish http://www.lecturasenpdf.com/post/yoga-clasico-34517.html
Check here in English ==> https://reishireview.cf/share/google-books-store-yoga-clasico-pdf-by-walter-gardini.html