Equal contributors Knut Brockmann, University of Göttingen 22 February 2013 Andreas Ohlenbusch and Simon Edvardson contributed equally to this work. By an oversight this was not designated in the authors´ list. Competing interests None declared
Equal contributors
22 February 2013
Andreas Ohlenbusch and Simon Edvardson contributed equally to this work. By an oversight this was not designated in the authors´ list.
Competing interests
None declared