Edit: e) by dle mě mohlo být takto:

<math> o(t) = \left\{

t \geq 2 \quad \ldots \quad i(t-2) 
  \quad\left\{
    \quad t-2 < 1 \Leftrightarrow t < 3 \quad\ldots\quad \frac{1}{2} 
    \\
    \quad t-2 \geq 1 \Leftrightarrow t \geq 3 \quad\ldots\quad 1
  \right.  
\\
t < 2 \quad\ldots\quad i(t)   
  \quad\left\{
    t < 1 \quad\ldots\quad \frac{1}{2}
    \\
    t \geq 1 \quad\ldots\quad 1      
  \right.  

\right. </math>