D. P. Parent is the author of a book of Exercises in Number Theory. Its authors are D. Barsky, F. Bertrandias, G. Christol, A. Decomps, H. Delange, J.-M. Deshouillers, K. Gérardin, J. Lagrange, J.-L. Nicolas, M. Pathiaux, G. Rauzy and M. Waldschmidt. The initials of the pseudonym recall the names of Delange, Pisot and Poitou, the three organizers of a Number Theory Seminar in Paris, which runs since 1959.