Ways to improve my understanding of CLisp and AI

Hi all.

I'm learning CLisp from the gigamonkeys book that's available online for free. What I'd like to know is how can improve my understanding of Lisp as well as how to write code for applications that use Artificial Intelligence? Say I would like to make an artificial neural network, just for kicks (this is purely an exercise for the sake of self-improvement, nothing more, nothing less), that filters spam or tries to study patterns in the movements of financial markets.

What steps can I take to improve my understanding of these two things? Any projects or applications I can learn from? Any suggestions?
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