new method "elim_to_cases" provides ad-hoc conversion of obtain-style
elimination goals to a disjunction of existentials.
structure ROOT =
struct
structure Nat =
struct
datatype nat = Zero_nat | Suc of nat;
fun less_nat n (Suc m) = less_eq_nat n m
| less_nat n Zero_nat = false
and less_eq_nat (Suc n) m = less_nat n m
| less_eq_nat Zero_nat m = 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*)
end; (*struct ROOT*)