Excerpt from Men at Arms by Terry Pratchett:
Cuddy’s breath turned to crystals in the air.
‘Oh, my,’ said Detritus. ‘I think this the pork
futures warehouse in Morpork Road.’
‘What?’
‘Used to work here,’ said the troll. ‘Used to
work everywhere. Go away, you stupid troll, you too
thick,’ he added, gloomily.
‘Is there any way out?’
‘The main door is in Morpork Street. But no one
comes in here for months. Till pork exists.’
Probably no other world in the multiverse has warehouses for things which only exist in potentia, but the pork futures warehouse in Ankh-Morpork is a product of the Patrician’s rules about baseless metaphors, the literal-mindedness of citizens who assume that everything must exist somewhere, and the general thinness of the fabric of reality around Ankh, which is so thin that it’s as thin as a very thin thing. The net result is that trading in pork futures—in pork that doesn’t exist yet—led to the building of the warehouse to store it in until it does. The extremely low temperatures are caused by the imbalance in the temporal energy flow. At least, that’s what the wizards in the High Energy Magic building say. And they’ve got proper pointy hats and letters after their name, so they know what they’re talking about.