Artur Czumaj Michelangelo Grigni Papa Sissokho Hairong Zhao Approximation schemes for minimum 2-edge-connected and biconnected subgraphs in planar graphs. 496-505 2004 conf/soda/2004 SODA http://doi.acm.org/10.1145/982792.982863 db/conf/soda/soda2004.html#CzumajGSZ04