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. 2014 Oct 14;9(10):e107763. doi: 10.1371/journal.pone.0107763

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This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

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In (a), node and its bottom-most neighbor are shown in dark blue. In (b), node , , are shown in green and node , , are shown in dark blue.

Inline graphic — In (a), node and its bottom-most neighbor are shown in dark blue. In (b), node , , are shown in green and node , , are shown in dark blue.