Alexander Grothendieck introduces from 1960 onward, at the Institut des Hautes Études Scientifiques in Paris, scheme theory, published in two major series: the Éléments de géométrie algébrique (EGA, with the collaboration of Jean Dieudonné, 1960-1967) and the Séminaire de géométrie algébrique (SGA, 1960-1969). Scheme theory completely generalizes and reformulates the foundations of algebraic geometry established by André Weil in 1946, further unifying it with much of number theory, and provides the technical apparatus — in particular étale cohomology — needed to tackle the Weil conjectures, which Pierre Deligne would finally prove in 1973-74. Grothendieck received the Fields Medal in 1966, but declined to travel to the Moscow congress to collect it in person, in protest of the Soviet Union's military expansion; his political activism also included teaching category theory classes in the forests near Hanoi while the city was being bombed, as a protest against the Vietnam War.