\section{Properties of Algebraic Extensions} \begin{theorem}[Algebraic over Algebraic Is Algebraic] If $\K$ is an algebraic extension of $\E$ and $\E$ is an algebraic extension of $\F$, then $\K$ is an algebraic extension of $\F$. \end{theorem} \begin{corollary}[Subfield of Algebraic Elements] Let $\E$ be an extension field of the field $\F$. Then the set of all elements of $\E$ that are algebraic over $\F$ is a subfield of $\E$. \end{corollary}