Ramification groups #
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The decomposition subgroup and inertia subgroups.
TODO: Define higher ramification groups in lower numbering
The decomposition subgroup defined as the stabilizer of the action
on the type of all valuation subrings of the field.
The valuation subring
A (considered as a subset of
is stable under the action of the decomposition group.
The multiplicative action of the decomposition subgroup on
The inertia subgroup defined as the kernel of the group homomorphism from
the decomposition subgroup to the group of automorphisms of the residue field of