test2 =
    runST $
    do
    t <- list_dubst [3,4,2,5,1]
    dubst_size t

-- illustrates how sharing of (even empty) subtrees breaks insertion
test2 =
    runST $
    do
    t <- list_dubst [3,4,2,5,1]
    dubst_size t

-- illustrates how sharing of (even empty) subtrees breaks insertion
test2 =
    runST $
    do
    t <- list_dubst [3,4,2,5,1]
    dubst_size t

-- illustrates how sharing of (even empty) subtrees breaks insertion