Question 76
In the parallelogram $ABCD$ we have $|AB| = |BD|$. Let $K$ be a point on the line $AB$ different from $A$, such that $|KD| = |AD|$. Denote the reflection of the point $C$ over $K$ by $M$, and the reflection of $B$ over $A$ by $N$. Prove that $MDN$ is an isosceles triangle with the apex at $D$.