"Post-Classical Developments in the Concepts of Karma and Rebirth in Theravada Buddhism." by Bruce Matthews. in Karma and Rebirth: Post-Classical Developments State Univ of New York Press: 1986 ISBN0-87395-990-6 pg 125;
Collins, Steven. Selfless persons: imagery and thought in Theravāda Buddhism Cambridge University Press, 1990. ISBN0-521-39726-X pg 215[1]