Cant make the spell...Can someone help plz?

Cant make the spell...Can someone help plz?

I'm new here and a beginning spellmaker.
But i cant figure out how to make this spell in GUI .
Name: A Eye For A Eye.
Effect: if a oppenent kills a unit from you, the killing unit get killd imideatly IF its in the aura range.
Can some1 help me

Unit Dies

condition-killing unit is within x of whichUnit

Actions

Kill ( KillingUnit )