global_qed: refrain from ProofContext.auto_bind_facts, to avoid
polluting the final result context with bindings involving loose
free variables;
structure ROOT =
struct
structure Codegen =
struct
fun lookup ((k, v) :: xs) l =
(if ((k : string) = l) then SOME v else lookup xs l)
| lookup [] l = NONE;
end; (*struct Codegen*)
end; (*struct ROOT*)