Let Γ be a group generated by two positive multi-twists. We give some sufficient conditions for Γ to be free or have no “unexpectedly reducible” elements. For a group Γ generated by two Dehn twists, we classify the elements in Γ which are multi-twists. As a consequence we are able to list all the lantern-like relations in the mapping class groups. We classify groups generated by powers of two Dehn twists which are free, or have no “unexpectedly reducible” elements. In the end we pose similar problems for groups generated by powers of n ≥ 3 twists and give a partial result.
Hamidi-Tehrani, Hessam  1
@article{10_2140_agt_2002_2_1155,
author = {Hamidi-Tehrani, Hessam},
title = {Groups generated by positive multi-twists and the fake lantern problem},
journal = {Algebraic and Geometric Topology},
pages = {1155--1178},
year = {2002},
volume = {2},
number = {2},
doi = {10.2140/agt.2002.2.1155},
url = {http://geodesic.mathdoc.fr/articles/10.2140/agt.2002.2.1155/}
}
TY - JOUR AU - Hamidi-Tehrani, Hessam TI - Groups generated by positive multi-twists and the fake lantern problem JO - Algebraic and Geometric Topology PY - 2002 SP - 1155 EP - 1178 VL - 2 IS - 2 UR - http://geodesic.mathdoc.fr/articles/10.2140/agt.2002.2.1155/ DO - 10.2140/agt.2002.2.1155 ID - 10_2140_agt_2002_2_1155 ER -
%0 Journal Article %A Hamidi-Tehrani, Hessam %T Groups generated by positive multi-twists and the fake lantern problem %J Algebraic and Geometric Topology %D 2002 %P 1155-1178 %V 2 %N 2 %U http://geodesic.mathdoc.fr/articles/10.2140/agt.2002.2.1155/ %R 10.2140/agt.2002.2.1155 %F 10_2140_agt_2002_2_1155
Hamidi-Tehrani, Hessam. Groups generated by positive multi-twists and the fake lantern problem. Algebraic and Geometric Topology, Tome 2 (2002) no. 2, pp. 1155-1178. doi: 10.2140/agt.2002.2.1155
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