6.4. Find all solutions of the inequality

$$
\cos ^{2018} x+\sin ^{-2019} x \leqslant \sin ^{2018} x+\cos ^{-2019} x
$$

belonging to the interval $\left[-\frac{\pi}{3} ; \frac{5 \pi}{3}\right]$.
Answer: $\left[-\frac{\pi}{3} ; 0\right) \cup\left[\frac{\pi}{4} ; \frac{\pi}{2}\right) \cup\left(\pi ; \frac{5 \pi}{4}\right] \cup\left(\frac{3 \pi}{2} ; \frac{5 \pi}{3}\right]$