ins :: (Eq a, Num a, DIM n) => SparseVector n a -> (Index, a) -> SparseVector n a
ins v (i, 0) = del (checkDim i v) i
ins :: (Eq a, Num a, DIM n) => SparseVector n a -> (Index, a) -> SparseVector n a
ins v (i, 0) = del (checkDim i v) i
ins v (i, 0) = del (checkDim i v) i