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Over the next few lectures we're going to 
advance study intermediate student 

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language and learn a new language 
construct called the local expression. 

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What local expressions let us do is to 
have definitions, functions and 

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constants, that are only available within 
one small part of the program. 

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Once we learn how local works, which 
we'll do over three short videos, then 

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we're going to look at two important ways 
to use local. 

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One has to do with organizing programs 
that are large or written by more than 

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one person. 
Another has to do with dealing with 

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important performance problems when we 
can't use local.