Credits to

• Denis Auroux: „Xournal“ for inspiration
  http://xournal.sourceforge.net/
   
• Michael Zimmermann: SVG drawing of set square
  http://commons.wikimedia.org/wiki/File:Set_square_Geodreieck.svg
   
• blackboard logo from Nuvola icon theme
  https://www.iconfinder.com/iconsets/nuvola2
   

Thanks to

• the JAVA community, especially „stack overflow“
  http://stackoverflow.com/questions/tagged/java
   
• the authors of „Geany“
  http://geany.org