semiring_numeral_0_eq_0, semiring_numeral_1_eq_1 now [simp], superseeding corresponding simp rules on type nat; attribute code_abbrev superseedes code_unfold_post
structure Codegen =
struct
val arbitrary_option : 'a option = NONE;
fun dummy_option [] = arbitrary_option
| dummy_option (x :: xs) = SOME x;
end; (*struct Codegen*)