scholarly journals Dehn’s algorithm for simple diagrams

2015 ◽  
Vol 24 (14) ◽  
pp. 1550074
Author(s):  
Charles Frohman ◽  
Joanna Kania-Bartoszynska
Keyword(s):  
Conjugacy Class ◽  
Disjoint Union ◽  
Closed Surface ◽  
Intersection Numbers ◽  
Closed Curves ◽  
Class A ◽  
Positive Genus ◽  
Monotonically Decrease ◽  
Standard Presentation ◽  
Closed Oriented Surface

Dehn gave an algorithm for deciding if two cyclic words in the standard presentation of the fundamental group of a closed oriented surface of positive genus represent the same conjugacy class. A simple diagram on a surface is a disjoint union of simple closed curves none of which bound a disk. If [Formula: see text] is a once punctured closed surface of negative Euler characteristic, simple diagrams are classified up to isotopy by their geometric intersection numbers with the edges of an ideal triangulation of [Formula: see text]. Simple diagrams on the unpunctured surface [Formula: see text] can be represented by simple diagrams on [Formula: see text]. The weight of a simple diagram is the sum of its geometric intersection numbers with the edges of the triangulation. We show that you can pass from any representative to a least weight representative via a sequence of elementary moves, that monotonically decrease weights. This leads to a geometric analog of Dehn’s algorithm for simple diagrams.

scholarly journals Filling of closed surfaces

2018 ◽  
Vol 10 (04) ◽  
pp. 897-913 ◽  
Author(s):  
Bidyut Sanki
Keyword(s):  
Disjoint Union ◽  
Mapping Class ◽  
Constructive Proof ◽  
Closed Curves ◽  
Closed Surfaces ◽  
Minimal Filling ◽  
Minimum Number ◽  
Genus Formula ◽  
Positive Integers ◽  
Closed Oriented Surface

Let [Formula: see text] denote a closed oriented surface of genus [Formula: see text]. A set of simple closed curves is called a filling of [Formula: see text] if its complement is a disjoint union of discs. The mapping class group [Formula: see text] of genus [Formula: see text] acts on the set of fillings of [Formula: see text]. The union of the curves in a filling forms a graph on the surface which is a so-called decorated fat graph. It is a fact that two fillings of [Formula: see text] are in the same [Formula: see text]-orbit if and only if the corresponding fat graphs are isomorphic. We prove that any filling of [Formula: see text] whose complement is a single disc (i.e. a so-called minimal filling) has either three or four closed curves and in each of these two cases, there is a unique such filling up to the action of [Formula: see text]. We provide a constructive proof to show that the minimum number of discs in the complement of a filling pair of [Formula: see text] is two. Finally, given positive integers [Formula: see text] and [Formula: see text] with [Formula: see text], we construct a filling pair of [Formula: see text] such that the complement is a union of [Formula: see text] topological discs.

Curves, Surfaces, and Hyperbolic Geometry

2017 ◽  
Author(s):  
Benson Farb ◽  
Dan Margalit
Keyword(s):  
Homotopy Class ◽  
Hyperbolic Geometry ◽  
Hyperbolic Plane ◽  
Closed Surface ◽  
Intersection Numbers ◽  
Hyperbolic Surfaces ◽  
Closed Curves

This chapter explains the basics of working with simple closed curves, focusing on the case of the closed surface Sɡ of genus g. When g is greater than or equal to 2, hyperbolic geometry enters as a useful tool since each homotopy class of simple closed curves has a unique geodesic representative. The chapter begins by recalling some basic results about surfaces and hyperbolic geometry, with particular emphasis on the boundary of the hyperbolic plane and hyperbolic surfaces. It then considers simple closed curves in a surface S, along with geodesics and intersection numbers. It also discusses the bigon criterion, homotopy versus isotopy for simple closed curves, and arcs. Finally, it describes the change of coordinates principle and three facts about homeomorphisms.

scholarly journals ISOTOPY AND HOMEOMORPHISM OF CLOSED SURFACE BRAIDS

2020 ◽  
pp. 1-10
Author(s):  
MARK GRANT ◽  
AGATA SIENICKA
Keyword(s):  
Braid Group ◽  
Class Group ◽  
Closed Surface ◽  
Orientable Surface ◽  
Mapping Class ◽  
Closed Orientable Surface ◽  
Outer Action ◽  
Positive Genus ◽  
Closed Sphere ◽  
Group Modulo

Abstract The closure of a braid in a closed orientable surface Ʃ is a link in Ʃ × S1. We classify such closed surface braids up to isotopy and homeomorphism (with a small indeterminacy for isotopy of closed sphere braids), algebraically in terms of the surface braid group. We find that in positive genus, braids close to isotopic links if and only if they are conjugate, and close to homeomorphic links if and only if they are in the same orbit of the outer action of the mapping class group on the surface braid group modulo its centre.

MINIMAL 3-BRAID REPRESENTATIONS

1994 ◽  
Vol 03 (02) ◽  
pp. 163-177 ◽  
Author(s):  
R. D. KEEVER
Keyword(s):  
Conjugacy Class ◽  
Canonical Form ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Minimal Representation ◽  
Class A ◽  
Minimal Representations ◽  
Necessary And Sufficient

This paper provides necessary and sufficient conditions for a representation of any 3-braid to be minimal (with regard to the number of crossings) and includes an algorithm to obtain such a representation, the number of distinct minimal representations of a given 3-braid, as well as a unique canonical form for each braid in B3. Also presented are necessary and sufficient conditions for any 3-string braid word to be a minimal representation of its conjugacy class. A canonical form for each conjugacy class in B3 is given.

scholarly journals Addendum: "(1, 2) and weak (1, 3) homotopies on knot projections"

2014 ◽  
Vol 23 (08) ◽  
pp. 1491001 ◽  
Author(s):  
Noboru Ito ◽  
Yusuke Takimura
Keyword(s):  
Personal Communication ◽  
Finite Collection ◽  
Closed Curves ◽  
Oriented Surface ◽  
Reidemeister Moves ◽  
Closed Oriented Surface

After this paper was published, the following information about doodles was pointed out by Roger Fenn. A doodle was introduced by Fenn and Taylor [2], which is a finite collection of closed curves without triple intersections on a closed oriented surface considered up to the second flat Reidemeister moves with the condition (*) that each component has no self-intersections. Khovanov [4] introduced doodle groups, and for his process, he considered doodles under a more generalized setting (i.e. removing the condition (*) and permitting the first flat Reidemeister moves). He showed [4, Theorem 2.2], a result similar to our [3, Theorem 2.2(c)]. He also pointed out that [1, Corollary 2.8.9] gives a result similar to [4, Theorem 2.2]. The authors first noticed the above results by Fenn and Khovanov via personal communication with Fenn, and therefore, the authors would like to thank Roger Fenn for these references.

scholarly journals AN ALGEBRAIC CHARACTERIZATION OF SIMPLE CLOSED CURVES ON SURFACES WITH BOUNDARY

2010 ◽  
Vol 02 (03) ◽  
pp. 395-417 ◽  
Author(s):  
MOIRA CHAS ◽  
FABIANA KRONGOLD
Keyword(s):  
Conjugacy Class ◽  
Fundamental Group ◽  
Intersection Number ◽  
Algebraic Characterization ◽  
Closed Curves ◽  
Curves On Surfaces

We prove that a conjugacy class in the fundamental group of a surface with boundary is represented by a power of a simple curve if and only if the Goldman bracket of two different powers of this class, one of them larger than two, is zero. The main theorem actually counts self-intersection number of a primitive class by counting the number of terms of the Goldman bracket of two distinct powers, one of them larger than two.

scholarly journals An algorithm to classify rational 3-tangles

2015 ◽  
Vol 24 (01) ◽  
pp. 1550004 ◽  
Author(s):  
B. Kwon
Keyword(s):  
Disjoint Union ◽  
Closed Curves ◽  
Curves On Surfaces

A 3-tangle T is the disjoint union of three properly embedded arcs in the unit 3-ball; it is called rational if there is a homeomorphism of pairs from (B3, T) to (D2 × I, {x1, x2, x3} × I). Two rational 3-tangles T and T′ are isotopic if there is an orientation-preserving self-homeomorphism h : (B3, T) → (B3, T′) that is the identity map on the boundary. In this paper, we give an algorithm to check whether or not two rational 3-tangles are isotopic by using a modified version of Dehn's method for classifying simple closed curves on surfaces.

scholarly journals Complexity of virtual multistrings

2021 ◽  
pp. 2150066
Author(s):  
David Freund
Keyword(s):  
Closed Curves ◽  
Oriented Surface ◽  
Text String ◽  
Type 3 ◽  
Closed Oriented Surface

A virtual[Formula: see text]-string [Formula: see text] consists of a closed, oriented surface [Formula: see text] and a collection [Formula: see text] of [Formula: see text] oriented, closed curves immersed in [Formula: see text]. We consider virtual [Formula: see text]-strings up to virtual homotopy, i.e. stabilizations, destabilizations, stable homeomorphism, and homotopy. Recently, Cahn proved that any virtual 1-string can be virtually homotoped to a minimally filling and crossing-minimal representative by monotonically decreasing both genus and the number of self-intersections. We generalize her result to the case of non-parallel virtual [Formula: see text]-strings. Cahn also proved that any two crossing-irreducible representatives of a virtual 1-string are related by isotopy, Type 3 moves, stabilizations, destabilizations, and stable homeomorphism. Kadokami claimed that this held for virtual [Formula: see text]-strings in general, but Gibson found a counterexample for 5-strings. We show that Kadokami’s statement holds for non-parallel [Formula: see text]-strings and exhibit a counterexample for general virtual 3-strings.

COMPLEX FENCHEL-NIELSEN COORDINATES FOR QUASI-FUCHSIAN STRUCTURES

1994 ◽  
Vol 05 (02) ◽  
pp. 239-251 ◽  
Author(s):  
SER PEOW TAN
Keyword(s):  
Teichmüller Space ◽  
Teichmuller Space ◽  
Closed Curves ◽  
Oriented Surface ◽  
Hyperbolic Structures ◽  
Embedded Image ◽  
Totally Real ◽  
Real Subspace ◽  
Closed Oriented Surface

Let Fg be a closed oriented surface of genus g ≥ 2 and let [Formula: see text] be the space of marked quasi-fuchsian structures on Fg. Let [Formula: see text] be a set of non-intersecting, non-trivial simple closed curves on Fg that cuts Fg into pairs of pants components. In this note, we construct global complex coordinates for [Formula: see text] relative to [Formula: see text] giving an embedding of [Formula: see text] into [Formula: see text]. The totally real subspace of [Formula: see text] with respect to these coordinates is the Teichmüller Space [Formula: see text] of marked hyperbolic structures on Fg, the coordinates reduce to the usual Fenchel-Nielsen coordinates for [Formula: see text] relative to [Formula: see text]. Various properties of the embedded image are studied.

Complete systems of surfaces in 3-manifolds

1997 ◽  
Vol 122 (1) ◽  
pp. 185-191 ◽  
Author(s):  
FENGCHUN LEI
Keyword(s):  
Finite Number ◽  
Boundary Component ◽  
Pairwise Disjoint ◽  
Complete System ◽  
Closed Surface ◽  
The Other ◽  
Closed Curves ◽  
Orientable Surfaces

A complete system (CS) [Jscr ]={J1, ..., Jn} on a connected closed surface F is a collection of pairwise disjoint simple closed curves on F such that the surface obtained by cutting F open along [Jscr ] is a 2-sphere with 2n-holes. Two CSs on F are equivalent if each can be obtained from the other via finite number of slides (defined in Section 1) and isotopies. Let M be a 3-manifold and F a boundary component of M of genus n. A CS of surfaces for M is a CS on F which bounds n pairwise disjoint incompressible orientable surfaces in M. When [Jscr ] is a CS of discs on the boundary of a handlebody V, it is well known that any CS on F which is equivalent to [Jscr ] is also a CS of discs for V. Our first result says that the same thing happens for a CS of surfaces for M, that is, if [Jscr ] is a CS of surfaces for M, then any CS equivalent to [Jscr ] is also a CS of surfaces for M. The following theorem is our main result on CS of surfaces in 3-manifolds:

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