[SOLVED] learning extension building

would you advice a book for learning joomla extension building?

Thank you in advance. I know that this kind of questions is not covered by the subscription, but may be you could be a cool person and share this kind of advice. Just as people do in south america

This is a great free beginners guide:

cocoate.com/jdev

There is also a video tutorial series on lynda.com (monthly subscription)

Thank you guys