Definition f' : BC :=
rec2 (BC_dummies 0 1 1 (sl - 1) g)
(comp2Ss cond nil [f'_cond; f'_nil; f'_then; f'_else] ).

Lemma f'_inf : arities f' = ok_arities 2 sl.
Definition f : BC :=
comp 1 sl f' [proj 1 0 0; proj 1 0 0]
(map (proj 1 sl) (seq 1 sl)).