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Answers for “平凡作用的核是什么?”

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For the trivial action ga=aga = a, the kernel is the entire group GG.

Conditions: The action is the trivial action ga=aga = a for all g∈Gg \in G and a∈Aa \in A.

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Yes, the S3S_3 permutation action on A={x1,x2,x3}A = \{x_1, x_2, x_3\} is faithful because its kernel is {1}\{1\}, the singleton containing only the identity element.

Conditions: G=S3G = S_3, the symmetric group of degree 3.; A={x1,x2,x3}A = \{x_1, x_2, x_3\}.; The action is defined by σxi=xσ(i)\sigma x_i = x_{\sigma(i)}.

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The kernel of the group action is the set of group elements gg such that ga=aga = a for all a∈Aa \in A. It is denoted as {g∣ga=a}\{g \mid ga = a\}.

Conditions: A group action of GG on AA is given.; The set consists of elements g∈Gg \in G satisfying the fixing condition for all a∈Aa \in A.

Meet the concept

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Yes, the map ga=aga = a for all g∈Gg \in G and a∈Aa \in A is a group action, known as the trivial action. It satisfies both the compatibility and identity properties of a group action.

Conditions: GG is a group and AA is a set.; The map is defined by ga=aga = a for all g∈Gg \in G and a∈Aa \in A.

Know when to use it

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A group action is called faithful when its kernel is exactly the singleton set containing only the identity element of GG, i.e., {g∣ga=a}={1}\{g \mid ga = a\} = \{1\}.

Conditions: The action has a kernel as defined in the video.; {1}\{1\} denotes the singleton containing the identity element of GG.