Lemma 34.3.3. Let T be an affine scheme. Let \{ T_ i \to T\} _{i \in I} be a Zariski covering of T. Then there exists a Zariski covering \{ U_ j \to T\} _{j = 1, \ldots , m} which is a refinement of \{ T_ i \to T\} _{i \in I} such that each U_ j is a standard open of T, see Schemes, Definition 26.5.2. Moreover, we may choose each U_ j to be an open of one of the T_ i.
Proof. Follows as T is quasi-compact and standard opens form a basis for its topology. This is also proved in Schemes, Lemma 26.5.1. \square
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