On the triangle-ABC,
Point-O is circumcenter, and point-H is orthocenter.
The middle point of OH is J.
Each the foot of perpendicular from A,B,C to BC,CA,AB is D,E,F.
Then, D,E,F and the middle points of AB,BC,CA,
furthermore, the middle points of AH,BH,CH, these 9points are on the same circle.
And the circle has J as the center of circle, of which the radius is the half of the
circumscribed circle of the triangle-ABC.
This circle is called 9points circle on the triangle-ABC.