Definition 11.1.3 (Convex Circled Hull).label Let $E$ be a vector space over $K \in \RC$ and $A \subset E$, then the set
\[\Gamma(A) = \bracs{\sum_{j = 1}^n t_j x_j \bigg | \seqf{t_j} \subset K, \seqf{x_j} \subset E, \sum_{j = 1}^n |t_j| \le 1 }\]
is the convex circled hull of $A$.