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Strongly-cyclic branched coverings of (1, 1)-knots and cyclic presentations of groups

Published online by Cambridge University Press:  26 June 2003

ALESSIA CATTABRIGA
Affiliation:
Department of Mathematics, University of Bologna, Piazza di Porta San Donato 5, 40126 Bologna, Italy. e-mail: cattabri@dm.unibo.it
MICHELE MULAZZANI
Affiliation:
Department of Mathematics, University of Bologna, Piazza di Porta San Donato 5, 40126 Bologna, Italy. e-mail: mulazza@dm.unibo.it

Abstract

We study the connections among the mapping class group of the twice punctured torus, the cyclic branched coverings of (1, 1)-knots and the cyclic presentations of groups. We give the necessary and sufficient conditions for the existence and uniqueness of the $n$-fold strongly-cyclic branched coverings of (1, 1)-knots, through the elements of the mapping class group. We prove that every $n$-fold strongly-cyclic branched covering of a (1, 1)-knot admits a cyclic presentation for the fundamental group, arising from a Heegaard splitting of genus $n$. Moreover, we give an algorithm to produce the cyclic presentation and illustrate it in the case of cyclic branched coverings of torus knots of type $(k,hk\pm 1)$.

Type
Research Article
Copyright
2003 Cambridge Philosophical Society

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