nominal lineage_a = ()
nominal root_branch = ()
nominal left_branch = ()
nominal right_branch = ()

union qtoken lineage branch =
    | QToken :: forall lineage branch. string -> qtoken lineage branch

inl split forall lineage.
    (token : qtoken lineage root_branch)
    : qtoken lineage left_branch * qtoken lineage right_branch =
    match token with
    | QToken label => QToken label, QToken label

inl merge forall lineage.
    (left : qtoken lineage left_branch)
    (right : qtoken lineage right_branch)
    : qtoken lineage root_branch =
    match left, right with
    | QToken _, QToken _ => QToken "branches-merged"

inl main () : string =
    inl root : qtoken lineage_a root_branch = QToken "root"
    inl left, _ = split root
    inl _ : qtoken lineage_a root_branch = merge left left
    "unreachable"