let subst_havoc m a =
let xzone = xzone_assigned a in
(* let v = L.fresh "v" (Mdata.Vmodel(Formula.ADT("bits",[]))) in
let bits = tbits_of_var v in *)
let new_vmh sigma =
let mb = L.apply sigma (F.var m.vbits) in
F.wrap (RtLib.havoc mb (Tint.term_of_xzone xzone))
in
[F.Update( m.vbits, new_vmh)]