Instance EqDec_statement: EqDec statement := eq_dec_statement.
Instance EqDec_external_function: EqDec external_function := eq_dec_external_function.

Lemma closed_Ssequence c1 c2 F: closed_wrt_modvars (Ssequence c1 c2) F <-> closed_wrt_modvars c1 F /\ closed_wrt_modvars c2 F.