Over the next few lectures we're going to 
advance study intermediate student 
language and learn a new language 
construct called the local expression. 
What local expressions let us do is to 
have definitions, functions and 
constants, that are only available within 
one small part of the program. 
Once we learn how local works, which 
we'll do over three short videos, then 
we're going to look at two important ways 
to use local. 
One has to do with organizing programs 
that are large or written by more than 
one person. 
Another has to do with dealing with 
important performance problems when we 
can't use local.