MathDB

In the parallelogram

ABCD

, rays are released from its vertices towards its interior. The rays coming out of the vertices

A{}

and

D{}

intersect at

E{}

and the rays coming out of the vertices

B{}

and

C{}

at point

F{}

. It is known that

\angle BAE=\angle BCF

and

\angle CDE = \angle CBF

. Prove that

AB \parallel EF

.
Proposed by V. Eisenstadt

Problem Statement