let narrow t1 t2 =
(* {initialized = t1.initialized || t2.initialized;
no_escaping_adr = t1.no_escaping_adr || t2.no_escaping_adr;
v = V.narrow t1.v t2.v
}
*)
create
((get_flags t1) lor (get_flags t2))
(V.narrow (get_v t1) (get_v t2))