Cowen's Theorem/Also presented as

Cowen's Theorem: Also presented as
Let $g$ be a progressing mapping.

There exists a class $M$ whose elements are exactly those $x$ which are elements of all classes that are superinductive under $g$.

Also:
 * $x \in M$ $x$ is an element of every subset of $\powerset x$ that:
 * contains $\O$
 * is closed under $g$ relative to $x$
 * is closed under chain unions.