\begin{definition}[Definition:Loop (Matroid)]
Let $M = \struct {S, \mathscr I}$ be a matroid.
A '''loop''' of $M$ is an element $x$ of $S$ such that $\set x$ is a dependent subset of $S$.
That is, $x \in S$ is a '''loop''' {{iff}} $\set x \not \in \mathscr I$.
\end{definition}