(2) Because CD‖AB‖EF ∠F=∠BAF, ∠C=∠CBA.

Because c and e are two different points on the circumference that are symmetrical ABout ab, f = c.

So ∠BAF=∠CBA, so CB‖AF is the same as AD‖BE, so the quadrilateral AMBN is a parallelogram.

It is easy to find ∠BAF=∠DAB and AB is ⊙ O diameter.

So the quadrilateral AMBN is a diamond.