> as lemmas

1878 W. C. Russell Auld Lang Syne I. iv. 60 This fiction declares that the happiest time of life is schoolboy time... A man need not be in a bad temper to deny this, recalling the kicks and tasks, the surly ushers, the tooth-splitting Greek, the brain-twisters of Euclid.

1922 John Martin's Big Bk. for Little Folk 256 Fascinating brain twisters never so hard as to discourage nor so easy as to fail of sustained interest.

1942 R. G. Collingwood New Leviathan xvi. 116 This is a famous brain-twister planted upon the world by Kant and Fichte.

1974 J. Marschak Econ. Information, Decision, & Predict. I. i. xvii. 357 But the ‘brain-twister’ puzzle at the end of the weekly paper will present these three objects in such a way that even a well-rested, college-educated reader may fail to recognize the identity between x and z.

1994 Minnesota Monthly Nov. 53/1 Besides juggling toys (torches, rings, knives), the store carries boomerangs, puzzles, brain-twister games, dominoes and darts, wind socks, and a wide assortment of flags.

2007 T. Stouffer Compl. Idiot's Guide World of Harry Potter iv. xi. 158 Rowling also mentions Golpalott's Third Law, which is a brain twister: ‘The antidote for a blended poison will be equal to more than the sum of the antidotes for each of the separate components.’