Two exercises on set theory about Cantor's equation and the von Neumann hierarchy Good evening to all.
I have two exercises I tried to resolve without a rigorous success:

*

*Is it true or false that if $\kappa$ is a non-numerable cardinal number then $\omega^\kappa = \kappa$,  where the exponentiation is the ordinal exponentiation?
I found out that the smallest solution for this Cantor's Equation is $\epsilon_0$ but it is numerable. I was thinking about $\omega_1$ but i don't know how to calculate something like $\omega^{\omega_1}$ and see if it is equal or not to $\omega_1$.


*Exists an ordinal number $\alpha > \omega$ that verify $\alpha \times \alpha \subseteq V_\alpha$ , where $V_\alpha$ is the von Neumann hierarchy?
Thanks in advance

You really just have to apply the definitions, in both cases, and see what happens.
For the first one, recall that the definition in the case of exponentiation is as follows: $$\alpha^0=1;\ \alpha^{\beta+1}=\alpha^\beta\cdot\alpha;\ \alpha^\delta=\sup\{\alpha^\gamma\mid\gamma<\delta\}.$$
Since $\kappa$ is a limit ordinal then we have that $\omega^\kappa=\sup\{\omega^\delta\mid\delta<\kappa\}$. It is a nontrivial claim that one should prove first, but $|\omega^\delta|=|\delta|$ for every infinite ordinal $\delta$. Now it's simple, since $\kappa$ is a cardinal, we have that $|\omega^\delta|=|\delta|<\kappa$ for $\delta<\kappa$, and so the supremum in the definition has to be $\kappa$.
As for the second problem, note that $\alpha\times\alpha=\{\{\{x\},\{x,y\}\}\mid x,y\in\alpha\}$. So you just have to verify what properties $\alpha$ has that $\{\{x\},\{x,y\}\}$ has rank smaller than $\alpha$. (Hint: what is the rank of $\{x\}$ and $\{x,y\}$?)
