entrytree_insert et (FirstUnder loc) eins =
    (fst $ entrytree_replace_f et loc f, loc_firstunder loc)
    where
        f e = ([e{entrytree_children = eins ++ entrytree_children e}], ())
entrytree_insert et (FirstUnder loc) eins =
    (fst $ entrytree_replace_f et loc f, loc_firstunder loc)
    where
        f e = ([e{entrytree_children = eins ++ entrytree_children e}], ())
entrytree_insert et (FirstUnder loc) eins =
    (fst $ entrytree_replace_f et loc f, loc_firstunder loc)
    where
        f e = ([e{entrytree_children = eins ++ entrytree_children e}], ())