Sl2-triple - Definition

Definition

Elements {e,h,f} of a Lie algebra g form an sl2-triple if

These commutation relations are satisfied by the generators

 h = \begin{bmatrix}
1 & 0\\
0 & -1
\end{bmatrix}, \quad
e = \begin{bmatrix}
0 & 1\\
0 & 0
\end{bmatrix}, \quad
f = \begin{bmatrix}
0 & 0\\
1 & 0
\end{bmatrix}

of the Lie algebra sl2 of 2 by 2 matrices with zero trace. It follows that sl2-triples in g are in a bijective correspondence with the Lie algebra homomorphisms from sl2 into g.

The alternative notation for the elements of an sl2-triple is {H, X, Y}, with H corresponding to h, X corresponding to e, and Y corresponding to f.

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