All things considered, there is something perverse about this Sunday afternoon. But the sun shines and makes you do things that are out of the ordinary. And on this day you follow a stranger into the Oxfam shop and watch as he browses a secondhand copy of The Divine Beauty of Mathematics. You kid yourself that this isn’t wrong. Strange maybe, but when he bends over to put it back on the bottom shelf, and purposely shows you the crack of his arse, then everything about this is okay.