“…A mathematical model of renormalization for perturbative quantum field theories, based on a commutative Hopf algebra H, a Rota-Baxter algebra R and the Birkhoff factorization of morphisms of commutative algebras φ : H → R, was developed in [7], [10], [11]. More recently, an approach to the theory of computation and the halting problem modelled on quantum field theory and renormalization was developed in [15], [16], [17], and further investigated in [9]. In view of applications to the theory of computation, it was observed in §4.6 of [15] that it would be useful to replace characters given by commutative algebra homomorphisms φ : H → R from the Hopf algebra to a Rota-Baxter algebra, with characters ψ : H → S with values in a min-plus semiring, satisfying ψ(xy) = ψ(x) + ψ(y) = ψ(x) ⊙ ψ(y).…”