Glencora Borradaile Philip N. Klein Claire Mathieu A Polynomial-Time Approximation Scheme for Euclidean Steiner Forest. 115-124 2008 FOCS http://dx.doi.org/10.1109/FOCS.2008.59 conf/focs/2008 db/conf/focs/focs2008.html#BorradaileKM08