We show that if S is a finite type orientable surface of negative Euler characteristic which is not the 3-holed sphere, 4-holed sphere or 1-holed torus, then EL.S/ is path connected, locally path connected and cyclic. 57M50; 57R30, 51M10, 20F65
IntroductionThe main result of this paper is the following:Theorem 0.1 If S is a finite type orientable surface of negative Euler characteristic which is not the 3-holed sphere, 4-holed sphere or 1-holed torus, then EL.S/, the space of ending laminations, is path connected, locally path connected and cyclic.EL.S/ is the space of filling, minimal geodesic laminations with the topology induced from ML.S/ by forgetting the measure. Equivalently, it has the coarse Hausdorff topology. See Definition 1.12. Interestingly, with respect to the Hausdorff topology, EL.S/ is totally disconnected as shown by Thurston [19, Section 10] and Zhu and Bonahon [22].Erica Klarreich [10] showed that if S is hyperbolic, then the boundary of the curve complex C.S/ is homeomorphic to the space of ending laminations on S . Therefore we have:Corollary 0.2 If S is a finite type orientable surface of negative Euler characteristic which is not the 3-holed sphere, 4-holed sphere or 1-holed torus, then @C.S/ is path connected, locally path connected and cyclic, where C.S/ is the curve complex of S .History For the thrice-punctured sphere S , C.S/ is trivial. It is well known that @C.S/ is totally disconnected when S is the 4-holed sphere or 1-holed torus. S is a once-punctured surface of genus at least two, then C.S / has exactly one end. With Leininger, he then showed [12] that EL.S/ is connected if S is any punctured surface of genus at least two or S is closed of genus at least 4. Leininger, Mj and Schleimer [11] showed that if S is a once-punctured surface of genus at least two then EL.S/ is both path connected and locally path connected.The idea of the proof is as follows. Given 0 ; 1 2 EL.S/ let 0 and 1 be measured laminations whose underlying laminations are 0 and 1 . Next, construct a path in ML.S / from 0 to 1 . A generic PL approximation of this path will yield a new path f 1 W OE0; 1 ! ML.S/ such that for each t , f 1 .t/ is an almost almost minimal almost filling measured lamination. That is, it has a sublamination f 1 .t/ without proper leaves whose complement supports at most a single simple closed geodesic. A measure of the complexity of this lamination is the length of the complementary geodesic, if one exists. We now find a sequence f 1 ; f 2 ; f 3 ; : : : such that the minimal length of all complementary geodesics to the f n .t/'s approaches infinity as n ! 1, provided such geodesics exist at all. After forgetting the measures, in the limit, we obtain the desired path in EL.S/ from 0 to 1 . (We don't worry about whether or not the f i 's converge to a path in ML.S/.) Since the final path can, in the appropriate sense, be taken arbitrarily close to the original (see Lemma 5.1), we obtain local path connectivity. Proving that the limit path is actually continuous requires control of the...