Algebraic Stack
Algebraic stacks describe families of geometric objects while retaining their automorphisms. Start with the three conditions in the definition and identify the separate roles of descent, the diagonal, and a smooth scheme atlas.
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Where to read
Start here: The Stacks Project — Algebraic stacks
The Stacks Project Authors · Online reference · English · Free full text
Section 94.12, Definition 94.12.1 and the comparison of smooth and étale scheme coverings
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Algebraic Geometry in the library · Preparation and skip guidance