Fixpoint sequence (cs: list statement) s :=
 match cs with
 | nil => s
 | c::cs' => Ssequence c (sequence cs' s)
 end.Fixpoint rsequence (cs: list statement) s :=
 match cs with
 | nil => s
 | c::cs' => Ssequence (rsequence cs' s) c
 end.

Lemma seq_assocN: forall {Espec: OracleKind} CS, forall Q Delta P cs s R, @semax CS Espec Delta P (sequence cs Sskip) (normal_ret_assert Q) -> @semax CS Espec Delta Q s R -> @semax CS Espec Delta P (sequence cs s) R.