Instance CompSpecs : compspecs.Definition Vprog : varspecs.Definition t_struct_elem := Tstruct _elem noattr.Definition t_struct_fifo := Tstruct _fifo noattr.Instance QS: listspec _elem _next (fun sh => malloc_token Ews t_struct_elem).

Lemma isnil: forall {T: Type} (s: list T), {s=nil}+{s<>nil}.