How can you get the list of all used variables and functions in

*To*: mathgroup at smc.vnet.net*Subject*: [mg91914] How can you get the list of all used variables and functions in*From*: Weber <a.pengwang at gmail.com>*Date*: Fri, 12 Sep 2008 05:30:07 -0400 (EDT)

How can you get the list of all used variables and functions in Mathematica? Is that possible?