Arithmetical proofs of strong normalization results for the symmetric λ μ-calculus

The symmetric $\lambda \mu$-calculus is the $\lambda \mu$-calculus introduced by Parigot in which the reduction rule $\m'$, which is the symmetric of $\mu$, is added. We give arithmetical proofs of some strong normalization results for this calculus. We show (this is a new result) that the $\mu\mu'$-reduction is strongly normalizing for the un-typed calculus. We also show the strong normalization of the $\beta\mu\mu'$-reduction for the typed calculus: this was already known but the previous proofs use candidates of reducibility where the interpretation of a type was defined as the fix point of some increasing operator and thus, were highly non arithmetical.