 Russell’s main contributions to logic and the foundations of mathematics include his discovery of  Russell’s paradox,  also known as the Russell-Zermelo paradox (Linsky 2013), his development (together with Whitehead) of the  theory of types,  his championing of logicism (the view that mathematics is, in some significant sense, reducible to formal logic), his impressively general theory of logical relations, his formalization of the mathematics of quantity and of the real numbers, and his refining of the first-order predicate calculus. 