Bourbaki

Example

Tag 09DS, permanent. Cite it as [Bourbaki, Tag 09DS].

Integration, chapter VII, § 1. Construction of a Haar measure

— 1) Let K=RK = \mathbf{R}. If s>0s > 0 then s⋅[0,1]=[0,s]s \cdot [0,1] = [0,s]; if s<0s < 0, s⋅[0,1]=[s,0]s \cdot [0,1] = [s,0]. Thus modRt=∣t∣\mathrm{mod}_\mathbf{R} t = |t| for all t∈Rt \in \mathbf{R}.

2) Let K=QpK = \mathbf{Q}_p. If s∈Qp∗s \in \mathbf{Q}_p^* is such that ∣s∣p=p−n|s|_p = p^{-n}, then sZps \mathbf{Z}_p is the set of x∈Qpx \in \mathbf{Q}_p such that ∣x∣p≤p−n|x|_p \leq p^{-n}; therefore, if μ\mu denotes the normalized Haar measure on Qp\mathbf{Q}_p, then μ(sZp)=p−n\mu(s \mathbf{Z}_p) = p^{-n}. Thus modQpt=∣t∣p\mathrm{mod}_{\mathbf{Q}_p} t = |t|_p for all t∈Qpt \in \mathbf{Q}_p.

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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Cites

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Transcribed from the printed volume. Not translated.