Given a square with side length $a$, we draw semicircles over each side such that they intersect at the center of the square. What is the area of the resulting four-leaf clover shape enclosed by the arcs?
Four semicircles together cover the resulting four-leaf clover in a double layer, while the remaining parts of the square are covered in a single layer. Therefore, the sum of the areas of the four semicircles exceeds the area of the square by exactly the area of the four-leaf clover.

Based on this, the area of the four-leaf clover is:

$$
t=4 \cdot \frac{\left(\frac{a}{2}\right)^{2} \pi}{2}-a^{2}=\frac{a^{2} \pi}{2}-a^{2}=a^{2}\left(\frac{\pi}{2}-1\right)
$$

For example, using a 10-digit approximation of $\pi \approx 3.1415926536$, we get $\left.t \approx 0.5708 a^{2}\right)$.

Uray László (Bp. V., Piarista g. II. o. t.)