 Jordan–Chevalley decomposition

Over an algebraically closed field, a linear operator $X$ has a unique decomposition into a commuting diagonalisable endomorphism $X_s$ and nilpotent endomorphism $X_n$. On its generalized eigenspace for $\lambda$, set $X_s=\lambda I$ and $X_n=X-\lambda I$. The Chinese remainder theorem makes both parts polynomials in $X$, so they preserve every $X$-invariant subspace. Uniqueness follows by restricting any other commuting decomposition to those generalized eigenspaces. Over a perfect field the semisimple part need only become diagonalizable after scalar extension.

The Jordan-Chevalley decomposition is a theorem in linear algebra concerning the structure of endomorphisms (or linear transformations) on a finite-dimensional vector space. It provides a way to decompose a linear operator into two simpler components: one that is semisimple and one that is nilpotent.