[XPerrata] Missing parentheses in example

At paragraph "3.7 For Expressions", example should be 

for $a in fn:distinct-values(book/author)
return ((book/author[. = $a])[1], book[author = $a]/title)

As example currently stands the result of the expression would be 

   <author>Stevens</author> 
  <author>Stevens</author> 
  <title>TCP/IP Illustrated</title> 
  <title>Advanced Programming in the Unix Environment</title> 
  <author>Abiteboul</author> 
  <title>Data on the Web</title> 
  <author>Buneman</author> 
  <title>Data on the Web</title> 
  <author>Suciu</author> 
  <title>Data on the Web</title> 

Emmanuel Lazinier
------------------------------------------------------------------
Chargé d'étude NTIC
DET/SMCO
8, bld Victor
00303 armées
Tel. 01.57.24.74.30
Fax. 01.57.24.82.85