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One way to formulate local class field theory is by saying that the local Artin map induces an isomorphism from the profinite completion of $K^\times$ to $\operatorname{Gal}(K^\text{ab}/K)$, which satisfy some commutative diagram relating the Artin maps of $K$ and $L$ when $L$ is a finite extension of $K$ (for example, the existence theorem correspond to the surjectivity of the induced map from the profinite completion).

In the global case, the Artin map becomes a map from the idèle class group $\mathbf{C}_K = \mathbb{A}_K^\times/K^\times$ to $\operatorname{Gal}(K^\text{ab}/K)$. My question is the following:

Is it true that, for a global field $K$, the Artin map induces an isomorphism from the profinite completion of $\mathbf{C}_K$ to $\operatorname{Gal}(K^\text{ab}/K)$?

I know that the global Artin map is subjective with kernel $\mathbf{C}_K^\circ$, the identity component of $\mathbf{C}_K$. Hence the question can be reformulated as:

Is it true that the profinite completion of $\mathbf{C}_K$ is equal to $\mathbf{C}_K/\mathbf{C}_K^\circ$?

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    $\begingroup$ $\varprojlim C_K/H$ but where $H$ ranges only over the open finite index subgroups? $\endgroup$ Commented Feb 21, 2022 at 23:24
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    $\begingroup$ Yes exactly I'm talking about profinite completion in this sense $\endgroup$ Commented Feb 22, 2022 at 0:59

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