An ordinal is woset, where for all members $a$ in the set, $a$'s segment is $a$ itself. But, the definition of $a$'s segment is:
$X_a=\{x\in X:x \subsetneq a\}$
But, given that definition, how can any ordinal set exist? If $a$ is a member of $X$, $X_a$ must be equal to $a$. But if that's true, then $a$ is a subset of itself and not equal to itself at the same time.
You're speaking as if $a\in X_a$, but that is never claimed.