Opaque div'_e.
Definition div_e : BC :=
comp 2 0 div'_e [comp 2 0 succ_e nil [proj 2 0 0]; proj 2 0 1] [proj 2 0 0].

Lemma div_correct v1 v2 :
unary v1 = true -> unary v2 = true ->
length (sem div_e [v1; v2] nil) = div (length v1) (length v2).