prop_insertSeq :: BagTest Int bag => bag Int -> Seq Int -> bag Int -> Bool
prop_insertSeq bag xs ys =
    insertSeq xs ys === union (fromSeq xs) ys
prop_insertSeq :: BagTest Int bag => bag Int -> Seq Int -> bag Int -> Bool
prop_insertSeq bag xs ys =
    insertSeq xs ys === union (fromSeq xs) ys
prop_insertSeq bag xs ys =
    insertSeq xs ys === union (fromSeq xs) ys