At what point does a harmless interest in collecting books become pathological? Perhaps when you start buying books you know you already have, in exactly the same edition, the same printing, in equally good condition. Virtually indistinguishable, in fact.
 
I decide, because a former student has been on my mind, to go to Southport. From Manchester you may take a direct train to Southport, but why would you do that when you can go via Liverpool, a city with three excellent dedicated second hand...