The Doflein Method for Violin Volume 1: The Beginning by Erich Doflein and Elma Doflein 68 page paperback This book contains quite a lot of duets along with technical exercises The myriad of duets, which range from Baroque to out-there 20th century stuff, get the student playing in harmony very early on There is some simple double-stop work, clapping exercises, exercises in which a student has to write a musical "answer" to a musical "question" Learn to navigate music that has repeats, DCs