This is a test article

$$S(f)(t)=a_{0}+\sum{n=1}{+\infty}{a_{n} \cos(n \omega t)+b_{n} \sin(n \omega t)}$$

and

$$\begin{aligned} abc &= def \\ abc &= def \end{aligned}$$

CO₂ + C → 2 CO

Hg²⁺ →[I^-] HgI₂ →[I^-] [Hg{II}I₄]^2-

H₂O

Y⁹⁹⁺

{227}_{90}Th⁺

A ⇔> B