Having complained some months ago about a grammatical solecism on huge signs displayed in the window of Blackwell’s shop in Broad Street, I was pleased to see that the mistake has been corrected in the posters put up in the marquee where the bookseller is operating at The Sunday Times Oxford Literary Festival. You may remember that the signs, for a Buy One Get One Free offer, featured an asterisked footnote saying “Cheapest item free”. Now the ‘Knowledge Retailer’ has amended this to read “Cheaper item free”. Good show. Now my first festival joke, offered by the biographer Richard Holmes during his thoroughly engaging interview with John Carey on Tuesday: “All power corrupts; Powerpoint corrupts absolutely.”