Kropholler, P. H.; Roller, M. A. (1989). "Relative ends and duality groups". Journal of Pure and Applied Algebra. 61 (2): 197–210. doi:10.1016/0022-4049(89)90014-5. MR1025923.
Kropholler, P. H.; Roller, M. A. (1989). "Relative ends and duality groups". Journal of Pure and Applied Algebra. 61 (2): 197–210. doi:10.1016/0022-4049(89)90014-5. MR1025923.