Minkowski Functional of Convex Absorbing Set is Finite

Theorem
Let $\GF \in \set {\R, \C}$.

Let $X$ be a vector space over $\GF$.

Let $A \subseteq X$ be a convex absorbing set.

Let $\mu_A$ be the Minkowki functional of $A$.

Then for each $x \in X$, $\map {\mu_A} x$ is a finite extended real number.

That is:
 * $\forall x \in X: \map {\mu_A} x < \infty$

Proof
Let $x \in X$.

From the definition of an absorbing set, there exists $t \in \R_{> 0}$ such that $x \in t A$, where $t A$ denotes the dilation of $A$ by $t$.

Then:


 * $t \in \set {t > 0 : t^{-1} x \in A}$

so that:


 * $\map {\mu_A} x \le t < \infty$