The lambda calculus forms a prototype universal programming language, which in its untyped version is related to Lisp, and has been treated in the first author's classic The Lambda Calculus (1984). The formalism has since been extended with types and used in functional programming (Haskell, Clean) and proof assistants (Coq, Isabelle, HOL), which are used to design and verify IT products and mathematical proofs. In this book, the authors focus on three classes of typing for lambda terms: simple types, recursive types and intersection types. Unexpected mathematical beauty is revealed in these three formalisms of terms and types. Numerous exercises are provided to deepen the reader's understanding and increase their confidence using types.

Henk Barendregt holds the chair on the Foundations of Mathematics and Computer Science at Radboud University, Nijmegen, The Netherlands.

Wil Dekkers is an Associate Professor in the Institute of Information and Computing Sciences at Radboud University, Nijmegen, The Netherlands.

Richard Statman is a Professor of Mathematics at Carnegie Mellon University, Pittsburgh, USA.