Alfred North Whitehead acknowledged Bergson's influence on his process philosophy in his 1929 "Process and Reality." However, Bertrand Russell, Whitehead's collaborator on "Principia Mathematica", was not so entranced by Bergson's philosophy. Although acknowledging Bergson's literary skills, Russell saw Bergson's arguments at best as persuasive or emotive speculation but not at all as any worthwhile example of sound reasoning or philosophical insight. The epistemologist Gaston Bachelard explicitly alluded to him in the last pages of his 1938 book "The Formation of the Scientific Mind". Others influenced by Bergson include Vladimir Jankélévitch, who wrote a book on him in 1931, Pierre Teilhard de Chardin, and Gilles Deleuze who wrote "Le bergsonisme" in 1966. Bergson also influenced the phenomenology of Maurice Merleau-Ponty and Emmanuel Levinas, although Merleau-Ponty had reservations about Bergson's philosophy. The Greek author Nikos Kazantzakis studied under Bergson in Paris and his writing and philosophy were profoundly influenced as a result.