Hiroshi Nagamochi Toshihide Ibaraki An Approximation for Finding a Smallest 2-Edge-Connected Subgraph Containing a Specified Spanning Tree. 31-40 http://dx.doi.org/10.1007/3-540-48686-0_3 1999 COCOON db/conf/cocoon/cocoon99.html#NagamochiI99