[ns] Where is the command "new" defined?

[ΥΤΕτ <b9973056@bupt.edu.cn>]

Hi everyone:
	I've just begun with my ns.But the first example seems not pleasing enough.
In the code : " %set ns [new Simulator] "
					***
It tells me "Invalide command name "new" ."
I really can't find where is the command "new" defined; Can you help me?

Best regards!

Zhao,peng