  A subalgebra of a Lie algebra $\mathfrak{h}\subset\mathfrak{g}$ determines
$\mathfrak{h}$-representation $\rho$ on
$\mathfrak{m}=\mathfrak{g}/\mathfrak{h}$. In this note we discuss how to
reconstruct $\mathfrak{g}$ from $(\mathfrak{h},\mathfrak{m},\rho)$. In other
words, we find all the ingredients for building non-reductive Klein geometries.
The Lie algebra cohomology plays a decisive role here.
