let rec get_var (x: var) (ar: act_ref) (b: b)
: rslt option =
assert (act_valid ar b);
let act = act_assoc_valid ar b in
begin if List.mem_assoc x act.act_vars then
Some(List.assoc x act.act_vars)
else
begin match act.act_parent with
| None -> None
| Some(ar1) -> get_var x ar1 b
end
end