insertL :: Ord k => k -> v -> MultiMap k v -> MultiMap k v
insertL k v (MM m) = MM (M.alter (Just . maybe (S.singleton v) (v S.<|)) k m)
insertL :: Ord k => k -> v -> MultiMap k v -> MultiMap k v
insertL k v (MM m) = MM (M.alter (Just . maybe (S.singleton v) (v S.<|)) k m)
insertL k v (MM m) = MM (M.alter (Just . maybe (S.singleton v) (v S.<|)) k m)