( 1) a？ =-a

Then a=0 or a=- 1.

If a = 0 and m = {0 0,0}, it contradicts the anisotropy of the set.

If a=- 1, M = {1,-1}, N = {1, -3}, MUN={ 1,-1, 3}

At this time, M∩N ={ 1}

(2) a? =2a- 1

At this time a= 1.

M={ 1, 1}, which contradicts the set.

(3)a=-a

At this time, a=0, m = {0,0}, which contradicts the anisotropy of the set.

(4)a=2a- 1

At this time, a= 1 M={ 1, 1}, which contradicts the anisotropy of the set.

To sum up, a=- 1, M∩N ={ 1}