 Although each blindspot is inaccessible, a disjunction of blindspots is normally not a blindspot. I can rationally believe that ‘Either the number of stars is even and I do not believe it, or the number of stars is odd and I do not believe it’. The author’s preface statement that there is some mistake in his book is equivalent to a very long disjunction of blindspots. The author is saying he either falsely believes his first statement or falsely believes his second statement or … or falsely believes his last statement.