X, m. (students’), un ——, a student at the Ecole Polytechnique. Aller À l’X, to go to that school. (Familiar) L’——, mathematics. Termed the “swat” by gentlemen cadets of the Royal Military Academy. Un ——, a thorough mathematician, one who devotes himself entirely to the study of mathematics. There is a story about a mathematician (some say he was no other than Arago) who used to work out problems wherever he found himself at the time they occurred to him. One day he was drawing figures with a piece of chalk on the back of a hackney coach when it began to move, but so wrapped up was he in his favourite occupation that he followed his extemporized blackboard at a walk at first, then at a run, but never stopped till he had found a solution of the problem. Un fort en ——, one well up in mathematics, but who knows little of other subjects. Une tÊte À ——, one who has a good head for mathematics. A pun on the formula ? ?, pronounced thÉta X.