How do you write square brackets in a system of equations in Latex?

Question

TeX

Hello!
Can you please tell me how to write square brackets in Latex?
PS I forgot to clarify: in the system of equations! Like these:

Answer 1

Something like this:

$\left[ 
      \begin{gathered} 
        x \le y; \\ 
        x < y, \\ 
      \end{gathered} 
\right.$