how can I put the same proposition in the main body and also in the appendix?

I couldn't find an answer of mine on this site, so I'll reproduce its code here:

documentclass{article}
usepackage{amsthm}
usepackage{thmtools, thm-restate}
 declaretheorem[name=Proposition]{proposition}

begin{document}

 begin{restatable}{proposition}{Firstprop}
   This is a proposition.
 end{restatable}

appendix
section{Proofs}
Firstprop*
  begin{proof}
  add my proof to this part qedhere
end{proof}

section{More results}
begin{proposition}
  This is another proposition.
end{proposition}

end{document} 

As you can see, I first nest a proposition in a restatable environment, defined by the thm-restate package. To the second argument of the environment (Firstprop) is associated a Firstprop* command, whch restates the proposition where it is used.