@Baker:
Thanks for the first and the second reference!

I already tried to study at fight.qc but it's really complex because it's melted down in the quake structure with think functions and company. I couldn't find the "core" of the functions where it says:"enemy is a player. go near to him, and everywhere he goes, chase him"
Can I simply define in the game
enemy = player?
I tried with enemy = classname==player but it's not correct
I'm total noob I know!

thanks again