[xsl] To find out immediate following tag

["J. S. Rawat" <jrawat@xxxxxxxxxxxxxx>]

Hi,
Anyone who can help me. I want to merge <a1> within <a> if it is 
immediate following it. "following::a1[1]" is not working properly.

Input
<a>first</a>
<a1>second</a1>
<a1>third</a1>
<a>fourth
<a1>fifth</a1>
<b1>sixth</b1>
</a>
<a1>seven</a1>
<a>eight</a>
<b1>nine</b1>
<a1>ten</a1>

OUTPUT
<a>first
second</a>
<a1>third</a1>
<a>fourth
<a1>fifth</a1>
<b1>sixth</b1>
seven</a>
<a>eight</a>
<b1>nine</b1>
<a1>ten</a1>