Stun when attacking from behind!

Stun when attacking from behind!

I want to know how to detect if a unit is attacking another unit from behind!
What are the angle combinations you use to do that.

Val > Facing of Attacked Unit - X and Val < Facing of Attacked Unit - Y

Explain Better!

srry, though i posted more, mbe my internet died or something

allright, check if the angle between the units is that. if it is, do w/e u want to the targ.

Oh, Sorry but...
I still not understanding!

Tell me step by step plz!