We present an explicitly typed lambda calculus "à la Church" based on the union and intersection types discipline; this system is the counterpart of the standard type assignment calculus "à la Curry." Our typed calculus enjoys Subject Reduction and confluence, and typed terms are strongly normal- izing when the universal type is omitted. Moreover both type checking and type reconstruction are decidable. In contrast to other typed calculi, a system with union types will fail to be "coherent" in the sense of Tannen, Coquand, Gunter, and Scedrov: different proofs of the same typing judgment will not necessarily have the same meaning. In response, we introduce a decidable notion of equality on type-assignment derivations inspired by the equational theory of bicartesian-closed categories.