Retrieved 22 March 2013. (subscription required) Short, pp. 50–53 Short, pp. 57 Short, pp. 57 and pp. 60 Holst, Gustav (April 1931).
Consultado o 22 de marzo de 2013.  (require subscrición) Short, pp. 50–53 Short, pp. 57 Short, pp. 57 e pp. 60 Holst, Gustav (April 1931).