Scope Question

Wow, I should really learn more about the scoping rules in Lisp. Any
suggested readings?

Anyhow, here's my current scope question:

Suppose I have a recursive function that is searching for elements in
a tree. How can I store a list such that it is not reset on each
recursive call to the search function?

In general, how can I initialize a variable within a function that
will not be reset on each recursive call to that function? I hope my
question is clear. If not, please let me know. Thanks.
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