Just now I was reading Thomas Cleary's translation of The Book of Five Rings. In the preface, written by Mr. Cleary, it is stated very little is known about the book's author, Miyamoto Mushashi. Almost everything we do know about him comes from The Book of Five Rings itself, according to the preface. It's also stated he's an undefeated duelist. So I started wondering: How certain is it that he was undefeated? Are we just going by his own account? How do we know he's being truthful, if so? Or, is there some sort of outside record we can consult to corroborate his claims?