Given two distinct points and in the plane, how many distinct points are there on the same plane such that is an equilateral triangle?
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If △ A B C is an equilateral triangle, it satisfies A B = A C and B A = B C . The set of points C that satisfy the first condition is a circumference with center A and radius A B , while the set of points C that satisfy the second condition is a circumference with center B and radius B A . Both circumferences intersect at two points, which are the only points C such that △ A B C is equilateral.