1https://bretionly.github.io/ertrASAS/BOOK1.html2https://bretionly.github.io/ertrASAS/BOOK2.html3https://bretionly.github.io/ertrASAS/BOOK3.html4https://bretionly.github.io/ertrASAS/BOOK4.html5https://bretionly.github.io/ertrASAS/BOOK5.html