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A strophoid is a general construction that derives a new curve $S$ from an original curve $C$ and two given points $O$ and $A$: given a point $P$ on $C$, the points $Q$ and $Q'$ of the strophoid lie on $OP$ at distance from $P$ equal to the distance $AP$. The description here is of the right strophoid, the strophoid of a straight line $\ell$ with respect to a point $O$ not on $\ell$ and $A$ the point of $\ell$ closest to $O$. See Lawrence [a2], pages 51 and 100. Richard Pinch (talk) 13:22, 11 December 2017 (CET)

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