Definition Equiv n:= forall k v blocks u 
   (G: Gen_loop_Zlist k v n = (blocks, u)) m
   (M: 32*(Z.of_nat n-1) < m <=32*(Z.of_nat n)),
   HMAC_DRBG_generate_helper_Z HMAC256 k v m = (u,flatten (rev blocks)).

Lemma E2: Equiv 2.