Deleuze passed the agrégation in philosophy in 1948, and taught at various lycées (Amiens, Orléans, Louis le Grand) until 1957, when he took up a position at the University of Paris. In 1953, he published his first monograph, "Empiricism and Subjectivity", on David Hume. This monograph was based on his 1947 DES ("") thesis, roughly equivalent to an M.A. thesis, which was conducted under the direction of Jean Hyppolite and Georges Canguilhem. From 1960 to 1964, he held a position at the Centre National de Recherche Scientifique. During this time he published the seminal "Nietzsche and Philosophy" (1962) and befriended Michel Foucault. From 1964 to 1969, he was a professor at the University of Lyon. In 1968, Deleuze defended his dissertations amid the ongoing May 68 demonstrations, and later published his two dissertations, "Difference and Repetition" (supervised by Gandillac) and "Expressionism in Philosophy: Spinoza" (supervised by Alquié).