@Funkyvaib
Yes, you are right. Some of the books are not for free and some you can find as PDF downloads in the net. There is not just one particular side/resource about them. It is really a basic mix of what I like and for what I also paid for beside other things. Did you read all the free PDF downloads and did you understand them? Give me a PM, tell me what you already did read and tell me what next book you like to read. Take care / DanPickUp