There are books on the subject. Can you believe that? Think about it. Either the book is no bloody good, in which case you follow its precepts and you and fifty thousand of your countrymen are slaughtered like geese at midwinter; or the book is true and authoritative and contains everything you need to know about the subject, in which case you follow its precepts and you and fifty thousand of your countrymen, see above, because the other side have read the same book and can predict your every move.