pub fn compute_position_and_nodes<'store, HAST, It: Iterator>(
    root: HAST::IdN,
    offsets: &mut It,
    stores: &'store HAST
) -> (Position, Vec<HAST::IdN>)where
    It::Item: Clone,
    HAST::IdN: Clone,
    HAST: HyperAST<'store>,
    HAST::T: WithSerialization + WithChildren<ChildIdx = It::Item>,