Classify the singularities (in the finite complex plane) of the following functions: (i) $\frac{1}{(\cosh z)^{2}}$; (ii) $\frac{1}{\cos (1 / z)}$; (iii) $\frac{1}{\log z} \quad(-\pi<\arg z<\pi)$; (iv) $\frac{z^{\frac{1}{2}}-1}{\sin \pi z} \quad(-\pi<\arg z<\pi)$.