discontinued slightly odd write_prv, which would still write .prv files the first time, and deprive add-on tools from date stamp change (cf. 157e74588c49);
structure Nat =
struct
datatype nat = Suc of nat | Zero_nat;
fun less_nat m (Suc n) = less_eq_nat m n
| less_nat n Zero_nat = false
and less_eq_nat (Suc m) n = less_nat m n
| less_eq_nat Zero_nat n = true;
end; (*struct Nat*)
structure Codegen =
struct
fun in_interval (k, l) n =
Nat.less_eq_nat k n andalso Nat.less_eq_nat n l;
end; (*struct Codegen*)