test1 =
    runST $
    do
    tp <- newSTRef DUEmpty
    dubst_insert_du 3 tp
    dubst_insert_du 5 tp
    t <- readSTRef tp
    dubst_size t
test1 =
    runST $
    do
    tp <- newSTRef DUEmpty
    dubst_insert_du 3 tp
    dubst_insert_du 5 tp
    t <- readSTRef tp
    dubst_size t
test1 =
    runST $
    do
    tp <- newSTRef DUEmpty
    dubst_insert_du 3 tp
    dubst_insert_du 5 tp
    t <- readSTRef tp
    dubst_size t