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Hi Again:
Let S_2, be the genus-2 connected, orientable surface, i.e.,
the connected sum of 2 tori (e.g., tori spelling and some other tori)
Consider a pair {C1,C2} of homologous, non-trivial curves, i.e.,
neither C1 nor C2 bounds, but C1-C2 is a (sub)surface in S_2.
Consider now a pair {D1,D2) of Dehn twists about each of C1,C2 ,
but in opposite directions; these Dehn twists about curves like
{C1,C2} are called bounding pairs. Still, for genus g=2, these
maps are trivial. Why is this so?
We clearly have only two classes of nonbounding curves , but I don't see
why , nor in what sense this map is trivial.
Any Ideas?
Thanks.
Let S_2, be the genus-2 connected, orientable surface, i.e.,
the connected sum of 2 tori (e.g., tori spelling and some other tori)
Consider a pair {C1,C2} of homologous, non-trivial curves, i.e.,
neither C1 nor C2 bounds, but C1-C2 is a (sub)surface in S_2.
Consider now a pair {D1,D2) of Dehn twists about each of C1,C2 ,
but in opposite directions; these Dehn twists about curves like
{C1,C2} are called bounding pairs. Still, for genus g=2, these
maps are trivial. Why is this so?
We clearly have only two classes of nonbounding curves , but I don't see
why , nor in what sense this map is trivial.
Any Ideas?
Thanks.