Valuable Hippopotamus Bibliography

There is a rise in interest in the Hippopotamus Defence.
In this brief post you will find  references of the Hippo bibliography not mentioned in the above mentioned Wikipedia link:

In 2006 the Italian FM De Santis published the book: "La Difesa Ippopotamo". The book is out of print now, but the editor is currently selling an ebook of it. 
At this link you can read a preview of this work.
The book has 146 pages, italian language, algebraic notation.
Highly recommended.
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Chapter 4 of GM Hillarp Persson'5 2005 book on the modern is fully devoted to the Hippo: that means 26 pages.

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FM Feustel's "Eroeffnungen-abseits aller Theorie" devotes 47 pages to the Hippo, mostly annotated games in german language, algebraic notation.
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In 2009 Nicholas Kostov compiled a free booklet on the Hippo. His work has been much appreciated:
http://www7.zippyshare.com/v/UttP91ZU/file.html