Custom proof environment preserving optional argument

Question

I basically want to obtain the result (replace Proof -> Solution, and mdframed around the environemnt) simply by the code:

\begin{solution}
    Set Theory Best Theory.
    \begin{align*}
        2 = \{\emptyset,\{\emptyset\},\{\emptyset,\{\emptyset\}\}\}
    \end{align*}
\end{solution}

This can be easily done using \renewenvironment. My main issue lies in preserving the optional argument in the proof environment, i.e. something like this would still work:

\begin{solution}[Proof]
    Set Theory Best Theory.
    \begin{align*}
        2 = \{\emptyset,\{\emptyset\},\{\emptyset,\{\emptyset\}\}\}
    \end{align*}
\end{solution}

Any help is greatly appreciated.

EDIT: To clarify, I do not have a working solution environment working. The first image above can be made possible by:

\newenvironment{solution}
  {\begin{mdframed}\begin{proof}[Solution]}
  {\end{proof}\end{mdframed}}

But it will not accept any arguments (so the second image will not be obtained)

Answer 1

Well, the answer is easy:

\newenvironment{solution}[1][Solution]
  {\begin{mdframed}\begin{proof}[#1]}
  {\end{proof}\end{mdframed}}

If you call \begin{solution}, you'll get “Solution” as the label; with \begin{Solution}[Hint] you'll get “Hint” as the label.