λμ-calculus and Λμ-calculus: a Capital Difference

Since Parigot designed the λμ-calculus to algorithmically interpret classical natural deduction, several variants of λμ-calculus have been proposed. Some of these variants derived from an alteration of the original syntax due to de Groote, leading in particular to the Λμ-calculus of the second author, a calculus truly different from λμ-calculus since, in the untyped case, it provides a Böhm separation theorem that the original calculus does not satisfy. In addition to a survey of some aspects of the history of λμ-calculus, we study connections between Parigot’s calculus and the modified syntax by means of an additional toplevel continuation. This analysis is twofold: first we relate λμ-calculus and Λμ-calculus in the typed case using λμtp-calculus, which contains a toplevel continuation constant tp, and then we use calculi of the family of λμt̂p-calculi, containing a toplevel continuation variable t̂p, to study the untyped setting and in particular relate calculi in the modified syntax.