Predual

In mathematics, particularly in functional analysis and the theory of operator algebras, a **predual** refers to a Banach space that serves as the dual space of another space. Specifically, if \( X \) is a Banach space, then a space \( Y \) is said to be a predual of \( X \) if \( X \) is isometrically isomorphic to the dual space \( Y^* \) of \( Y \).