APA

Heyel C., .Human-relations manual for executives. New York: McGraw-Hill Book Co.

Chicago

Heyel Carl, .Human-relations manual for executives. New York: McGraw-Hill Book Co.

Harvard

Heyel C., .Human-relations manual for executives. New York: McGraw-Hill Book Co.

MLA

Heyel Carl, .New York: McGraw-Hill Book Co. .