statistice using xsl

suppose i have the following xml file

<books>
<book>
   <author> joe
</author>
  <author> mary </author>
</book>
<book>
   <author> joe </author>
<author> hanz </author>
</book>
</books>

i need to perform the following
statistics using xsl

<tag name="joe">
 <path> book/author </path> <frequency>
4 </frequency>
<value  frq="2"  transactions = "1" , "2"> joe </value>
<value
frq="1" transactions = "1" > mary </value>
<value frq="1" transactions = "2" >
hanz </value>
</tag>

i mean joe has been repeated twice in book 1 and book 2,
while hanz has been repeated in book 2 only, i need to extract the order of
node book

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