## Problem C: 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.

### Sample input

1
8
1 10
3 6
6 8
6 2
3 -4
1 0
-2 -2
-2 4

### Output for sample input

yes

*Adapted from VI AMPwPZ by P. Rudnicki*

ACPC 2003