Paul Cohen proves in 1963, in Proceedings of the National Academy of Sciences, that the continuum hypothesis is independent of the Zermelo-Fraenkel axioms with the axiom of choice (ZFC): it can neither be proved nor disproved from them. To do so, Cohen develops the "forcing" technique, an entirely new method for constructing models of set theory that would become a standard tool of later mathematical logic. Together with Kurt Gödel's earlier result (1940, showing the hypothesis is consistent with ZFC), Cohen's work completes the determination of the logical status of one of the oldest problems in set theory, originally posed by Cantor in 1878. Cohen received the Fields Medal in 1966, still, as of this entry, the only mathematician awarded the prize for a work in mathematical logic.