“与”符曲线(英语:Ampersand curve)是二维平面内的一种四次曲线,因形状酷似“&”号而得名。其曲线方程为:
![Thumb](http://upload.wikimedia.org/wikipedia/commons/thumb/5/56/Ampersandcurve.svg/250px-Ampersandcurve.svg.png)
假若在方程右边加一个足够小的正常数,则曲线会断成四个闭合的连通分支,此时曲线在实域上有28条互异的双切线,[1]是实平面上四次曲线的双切线数目的最大可能值。
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