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Hello!
Please help me to write the following sentence right way:

When Jack was 67, he wrote "One Hundred Miles", the book about his philosophy of life.

I underlined the questionable elements of the sentence. I have two questions:
1. Which article should I use before "book", "a" or "the"?
2. Which word combination is better, "philosophy of life" or "life philosophy", or maybe "philosophy of living"?

Thanks.

a book
philosophy of life

Note that "the book" could be ok if you had previously mentioned that all through his life Jake planned to write "a book about his philosophy of life".

Josef, thank you very much.