share same child element in DTD

Hi,
  I'm new to xml and am trying to create a dtd. I want to know is it possible to share the same child element with different child elements by two parent elements. If yes, Any solution? 

Case:

DTD:
<!Element A (child) >
<!Element B (child) >
<!Element child (elt1, (elt2 | elt3)) >

XML:
<A><child>
 <elt1></elt1>
 <elt2></elt2>
</chiild></A>
<B><child>
 <elt1></elt1>
 <elt3></elt3>
</chiild></B>

Thanks a lot
Ray