Herman Grooten: Key concepts of Chess – The Hedgehog - A review
The "hedgehog" structure is a very resistant structure that also offers many possibilities for active play. It is not the specific variations that are important, but the knowledge of the typical ideas and plans. Dutch coach Herman Grooten teaches this in his Fritztrainer course "Key concepts of Chess - The Hedgehog". Philipp Hillebrand had a look at the course.
Source: chessbase.com