Levi, D., Olver,Peter, Thomova, Z., & Winternitz, P. (2011). Symmetries and integrability of difference equations. Cambridge University Press.

Levi, D., Olver,Peter, Zora Thomova, and Pavel Winternitz. Symmetries and Integrability of Difference Equations. Cambridge ; New York: Cambridge University Press, 2011.

Levi, D., et al. Symmetries and Integrability of Difference Equations. Cambridge University Press, 2011.