[texhax] Nested lists numbering

[Ivan Ivanov]

Dear colleagues,
I have the following question concerning nested enumerate environments. I have
\begin{enumerate}
\item Item 1
\item Item 2
  \begin{enumerate}
    \item Item 1.1
    \item Item 1.2
  \end{enumerate}
\end{enumerate}

The dvi ouput is 
1. Item 1
2. Item 2
     (a) Item 1.1
     (b) Item 1.2

and I would like it to be
1. Item 1
2. Item 2
     2.1. Item 1.1
     2.2. Item 1.2

I played to do it with \theenumi and \theenumii commands but I did not
find a solution.

Thank you very much for your help in advance.

Regards 
Ivan Ivanov