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I have to following Lie Algebra $L=\{x\in End(\mathbb{C}^6)\colon x^tS+Sx=0\}$, where $S=[\begin{smallmatrix} 0&I_3 \\ I_3&0 \end{smallmatrix}]$, and the subalgebra $H$ given by the diagonal elements in $L$.
I have found a basis of $L$ and $H$, which are, respectively:
$B_L=\{e_{ij}-e_{i+3j+3},...