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Center of symmetry
Given is a set of n points with integer coordinates. Your task is to decide whether the set has a center of symmetry.
A set of points S has the center of symmetry if there exists a point s (not necessarily in S) such that for every point p in S there exists a point q in S such that p-s = s-q.
The first line of input contains a number c giving the number of cases that follow. The first line of data for a single case contains number 1 <= n <= 10000. The subsequent n lines contain two integer numbers each which are the x and y coordinates of a point. Every point is unique and we have that -10000000 <= x, y <= 10000000.
For each set of input data print yes if the set of points has a center of symmetry and no otherwise.
1 8 1 10 3 6 6 8 6 2 3 -4 1 0 -2 -2 -2 4
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