My mathesoterica library. A friend wanted information about Catalan numbers (ordinarily I'd be glad you asked, but this time I don't know the answer and today I didn't have a chance to find out!), and this meant searching through my library of mathematical miscellany. There was a risk in glancing at these neglected friends: normally I would be distracted into reading them, and before long I'd be off "pafnutying" ("pafnuty" means to pursue tangential matters with hobby-like zeal, a word that has its origins in the slim pale blue volume called The Thread that is actually visible in the middle of the top row (Pafnuty was Tschebycheff's/Chebychev's first name (you can Google Tschebycheff/Chebychev (because this has already become too waffly and parenthetical) but you may have difficulty because it's a Russian name and it's not always Anglicised consistently (which is one of the threads in The Thread)))).