(: All bib items that are cited in bib items that are cited in books written this year by Priscilla Walmsley :)
declare namespace b = "http://www.massimop.eu/bib";

id(id(//b:author[b:name="Priscilla" and b:surname="Walmsley"]/ancestor::b:book[b:year="2007"]//b:reference/@b:idref)//b:reference/@b:idref)