let fold_bases f m acc =
match m with
Top(Top_Param.Set t, _) ->
let acc = if Null_Behavior.zone then acc else f K.null acc in
(Top_Param.O.fold f t acc)
| Top(Top_Param.Top, _) ->
raise Error_Top
| Map m ->
M.fold (fun k _ acc -> f k acc) m acc