declare
fun {Prime I}
   local
      fun {Help I AD}
     if I<1 then false
     elseif AD<2 then true
     elseif I mod AD == 0 then false
     else {Help I AD-1}
     end
      end
   in {Help I I-1}
   end
end

{Show {Prime 0}}
{Show {Prime 12}}
{Show {Prime 31}}