theorem about 6 points on a circle
- Let ABC be the triangle, and w to be circle that intersects all
its sides (AB in C1 and C2, AC in B1 and B2, BC in A1 and A2). Let A3 be
the point of intersection of tangent lines to w from A1 and A2, the same
definition for B3 and C3. Prove that lines A-A3, B-B3 and C-C3 are
Source: Alexey Zaslavsky.