http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
A 3-approximation algorithm for radiocoloring k-level restricted hierarchically specified planar graphs
Maria Andreou, Dimitris Fotakis, Sotiris Nikoletseas, Vicky Papadopoulou, Paul Spirakis