%% -*-BibTeX-*- @Article{GroetschelPadberg1979b, author = "Martin Gr{\"o}tschel and Manfred W. Padberg", title = "On the symmetric travelling salesman problem {II}: lifting theorems and facets", journal = "Mathematical Programming", volume = "16", pages = "281--302", year = "1979", classmath = "*90C10 52Bxx 52A40", language = "English", }