Let $M = (X, d)$ be a D1107: Metric space such that
(i) | $f : X \to X$ is a D49: Proper contraction on $M$ |
Then
\begin{equation}
\# \{ x \in X : f(x) = x \}
\leq 1
\end{equation}
(i) | $f : X \to X$ is a D49: Proper contraction on $M$ |