Definition 29.4.4. Let X be a scheme. Let Z, Y \subset X be closed subschemes corresponding to quasi-coherent ideal sheaves \mathcal{I}, \mathcal{J} \subset \mathcal{O}_ X. The scheme theoretic intersection of Z and Y is the closed subscheme of X cut out by \mathcal{I} + \mathcal{J}. The scheme theoretic union of Z and Y is the closed subscheme of X cut out by \mathcal{I} \cap \mathcal{J}.
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Comment #3179 by Jonathan Gruner on
Comment #3292 by Johan on