comparing 2 strings from different elements

Doing an assignment. Tearing my hair out.
I'm kinda new to XML. I have a bookshop system as shown below:

<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet type="text/xsl" href="Bookstore.xsl"?>
<Bookstore>
<Book>
<Author>Mohandas K. Gandhi</Author>
<Title>An Autobiography, Or, The Story of My Experiments with Truth</Title>
<Publisher>Penguin</Publisher>
<ISBN>0140066268</ISBN>
<Price Currency="GBP">7.19</Price>
</Book>
<Book>
<Editor>Carl G. Jung</Editor>
<Contributors>
<Author>Carl G. Jung</Author>
<Author>Joseph L. Henderson</Author>
<Author>M.-L. von Franz</Author>
<Author>Aniela Affé</Author>
<Author>Jolande Jacobi</Author>
</Contributors>
<Title>Man and His Symbols</Title>
<Publisher>Picador</Publisher>
<ISBN>0330253212</ISBN>
<Price Currency="EUR">16.30</Price>
</Book>
<Book>
<Author>Donald E. Knuth</Author>
<Title>The Art of Computer Programming</Title>
<Volume>1</Volume>
<Edition>3rd</Edition>
<Publisher>Addison-Wesley</Publisher>
<ISBN>0201898834</ISBN>
<Price Currency="USD">54.99</Price>
</Book>
</Bookstore>

I want the name of the editor Carl G. Jung to appear only once.
How can I compare the values of Editor and Contributors?

Welcome to the forums, please use &#91code][/code] tags around code so it is easier to read.

So you've listed the editor, and then you list the contributors, but you don't want to list the contributor if the name matches that of the editor?

Show your XSL.