Citazione Stile APA (7a Edizione)

Butterfiel, W. (1964). Effective personal letters (2nd rev.). Prentice Hall.

Citazione stile Chigago Style (17a edizione)

Butterfiel, W. Effective Personal Letters. 2nd rev. Englewood Cliffs: Prentice Hall, 1964.

Citatione MLA (9a ed.)

Butterfiel, W. Effective Personal Letters. 2nd rev. Prentice Hall, 1964.