Mock, V. E. (1982). Subtraction drill for levels 1-3. David S. Lake Publishers.
Lua i Stíl Chicago (17ú heag.)Mock, Valerie E. Subtraction Drill for Levels 1-3. Belmont, Calif: David S. Lake Publishers, 1982.
Lua MLA (9ú heag.)Mock, Valerie E. Subtraction Drill for Levels 1-3. David S. Lake Publishers, 1982.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.