Let

is a convex quadrilateral.

is circumcircle of the triangle

.

and

are the intersection points of

with the segments

and

, respectively.

is the circumcircle of the triangle

.

is the intersection point of the diagonals and

is the intersection point of the segment

with

.

is the intersection point of

and the circumcircle of the triangle

.

is the intersection point of

and the diagonal

. Prove that the points

,

,

,

and the points

,

,

,

are concyclic.
It is a harder problem, related to the problem above.