Groups with small Dehn functions and bipartite chord diagrams
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- Ol’shanskii, A.Y. & Sapir, M.V. GAFA, Geom. funct. anal. (2006) 16: 1324. doi:10.1007/s00039-006-0580-9
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We introduce a new invariant of bipartite chord diagrams and use it to construct the first examples of groups with Dehn function n2log n. Some of these groups have undecidable conjugacy problem. Our groups are multiple HNN extensions of free groups. We show that n2log n is the smallest Dehn function of a multiple HNN extension of a free group with undecidable conjugacy problem.