1 \documentclass{article}

     2 \usepackage[ruled,vlined]{algorithm2e}

     3  

     4 \begin{document}

     5 \begin{algorithm}[H]

     6 \SetAlgoLined

     7 \KwResult{rexp }

     8  Compute list $l_1: [r_1\backslash c_1 \cdots c_n, r_1\backslash c_1 \cdots c_{n-1}, ..., r_1 \backslash c_1, r_1]$\;

     9  Compute list $l_2: [r_2, r_2\backslash c_n, r_2\backslash c_{n-1} c_{n}, ..., r_2 \backslash c_1\cdots c_n]$\;

    10  Compute list $l_3$: 

    11  $l_3 \gets []$ \;

    12  \For{$i\gets1$ \KwTo $n$}{

    13     $\mathit{if} \; \mathit{nullable}(r_1 \backslash c_1 \cdots c_{n-i+1}) \; \mathit{then} \; \mathit{add} \; i \; \mathit{to} \; l_3$

    14     }

    15     $result \gets r_1 \backslash c_1 \cdots c_n \cdot r_2$\\

    16  \For{$i\gets0$ \KwTo $l_3.length -1$}{

    17  $result \gets \mathit{ALT}(result, l2[l3[i]])$

    18  }

    19  \Return result

    20  \caption{ders2forSEQ($r_1$,$r_2$,$s$)}

    21 \end{algorithm}

    22 \end{document}