let rec retrieve tree term pos =
match tree with
| DiscriminationTree.Node (Some s, _) when pos = [] -> s
| DiscriminationTree.Node (_, map) ->
let res =
let rec retrieve tree term pos =
match tree with
| DiscriminationTree.Node (Some s, _) when pos = [] -> s
| DiscriminationTree.Node (_, map) ->
let res =