Eales, Richard (1985), Chess, The History of a Game, B.T. Batsford, pp. 73 ff., ISBN 0-7134-4607-2 Hooper, David; Whyld, Kenneth (1996), "Göttingen manuscript", The Oxford Companion to Chess (2 ed.), Oxford University, p. 156, ISBN 0-19-280049-3 Murray, H. J. R. (1913), A History of Chess, Oxford University Press, pp. 782–784, ISBN 0-19-827403-3