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math.GT2026
The first Galois obstruction in the Johnson cokernel
Shigeyuki Morita, Takuya Sakasai, Masaaki Suzuki
We explicitly determine the first Galois obstruction in the cokernel of the Johnson homomorphism of the mapping class group of a surface of genus , for every genus . It…
math.GT2005
Homology cylinders and the acyclic closure of a free group
Takuya Sakasai
We give a Dehn-Nielsen type theorem for the homology cobordism group of homology cylinders by considering its action on the acyclic closure, which was defined by Levine, of a free…