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**Week thirty-seven: LIMACON (probability 9386)**, by David Sutton

LIMACON is a type of mathematical curve, to be precise a curve whose polar equation is r=acosθ+b. It has the form of a snail, hence its name, from the Latin limax, snail or slug. The C is soft and is properly written with a cedilla. It is sometimes called the limacon of Pascal, the Pascal in this case being not Blaise but his dad Etienne, though the artist Durer had discovered it before that.

There are quite a few names for mathematical curves, which will be old hat to you if you are a mathematician but pretty recherche if you are not. Congratulations if you know the difference between, and can give the mathematical formulae for, AXOID, CISSOID, CONCHOID, CYCLOID, CARDIOID, HELICOID, SINUSOID and TROCHOID. The rest of will just have to file them mentally under 'some sort of mathematical thingy', and resolve that given another lifetime we really will get to grips with that mathematical stuff...