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The Stacks project

Example 87.19.11. Let B be a weakly admissible topological ring. Let B \to A be a ring map (no topology). Then we can consider

A^\wedge = \mathop{\mathrm{lim}}\nolimits A/JA

where the limit is over all weak ideals of definition J of B. Then A^\wedge (endowed with the limit topology) is a complete linearly topologized ring. The (open) kernel I of the surjection A^\wedge \to A/JA is the closure of JA^\wedge , see Lemma 87.4.2. By Lemma 87.4.10 we see that I consists of topologically nilpotent elements. Thus I is a weak ideal of definition of A^\wedge and we conclude A^\wedge is a weakly admissible topological ring. Thus \varphi : B \to A^\wedge is taut map of weakly admissible topological rings and

\text{Spf}(A^\wedge ) \longrightarrow \text{Spf}(B)

is a special case of the phenomenon studied in Lemma 87.19.8.


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