[ns] where can i find the "set" code?

[Nick Zando]

Hi all,
i'd like to know where can i find the code in the tcl lib that is used to
start a ns script?
i mean:

set ns [new Simulator]
set nf [open trace.tr w]

Where can i find the code that is execute when i invoke the "set" keyword?

thanks in advance.

Nicola