You are not supposed to get it. It's a paradox. All of mathematics is built on paradoxes. That's the biggest paradox of all-all this orderliness, and at the heart, impossibility. Contradiction. Heaven built on the foundations of hell.

Novels are forged in passion, demand fidelity and commitment, often drive you to boredom or rage, sleep with you at night. They are the long haul. They are marriage. Stories, on the other hand, you can lose yourself in for a few weeks and then wrap up, or grow tired of and abandon and (maybe) return to later. They can cuddle you sweetly, or make you get on your knees and beg.

We all spend so much time worrying about the future that the present moment slips right out of our hands. And so all we have left is retrospection and anticipation, retrospection and anticipation. In which case what's left to recall but past anticipation? What's left to anticipate but future retrospection?

It is so common to write autobiographical fiction in which your own experience is thinly disguised.

'You might think of combinatorics as a machine too', the major says. 'A different sort of machine, though. Have you heard of Babbage's analytic engine? He never built it. ... I have an analytic machine of my own-right here.' He taps his own skull.

I could hear the knock and whistle of the water pipes, the purr of the calico cat. And at that moment a happiness filled me that was pure and perfect and yet it was bled with despair - as if I had been handed a cup of ambrosial nectar to drink from and knew that once I finished drinking, the cup would be withdrawn forever, and nothing to come would ever taste as good.

Obviously any fiction is going to be a combination of what is invented, what is overheard, what is experienced, what is experienced by people close to you, what you are told, what you have read, all mixed together into this kind of soup which, like any good soup, at the end you cannot really distinguish the ingredients.