Reverse things in XML using xslt

Hi I am learning for an exam where we should be able to reverse things in XML. I am trying to reverse the order of books, or reverse the order of elements in those books.

The input XML is:

   <library>
    <book>
      <author>James Joyce</author> 
      <title>Ulysses</title>
      <year>1922</year>
    </book>
    <book>
      <author>Alois Jirasek</author> 
      <title>Psohlavci</title>
      <year>1910</year>
    </book>
    <book>
      <author>Tomas Hruska</author> 
      <title>Pascal pro zacatecniky</title>
      <year>1989</year>
    </book>
  </library>

Reversed order of books:

   <library>
    <book>
      <author>Tomas Hruska</author> 
      <title>Pascal pro zacatecniky</title>
      <year>1989</year>
    </book>
    <book>
      <author>Alois Jirasek</author> 
      <title>Psohlavci</title>
      <year>1910</year>
    </book>
    <book>
      <author>James Joyce</author> 
      <title>Ulysses</title>
      <year>1922</year>
    </book>
  </library>

Reversing order of items in books:

   <library>
    <book>
      <year>1922</year>
      <title>Ulysses</title>
      <author>James Joyce</author>
    </book>
    <book>
      <year>1910</year>
      <title>Psohlavci</title>
      <author>Alois Jirasek</author> 
    </book>
    <book>
      <year>1989</year>
      <title>Pascal pro zacatecniky</title>
      <author>Tomas Hruska</author> 
    </book>
  </library>

I've been told that it should be quite easy, so don't try anything too fancy. I am allowed to use basic loops via for-each or recursion via apply-templates and also value-of.