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The first purpose of schemes theory is the geometrical study of solutions of algebraic systems of equations, not only over the real/complex numbers, but also over integer numbers (and more generally over any commutative ring with 1). It was finalized by Alexandre Grothendieck, during the 1950s and the 1960s.

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Are higher etale homotopy groups topological groups in a natural way?

If you choose to see profinite groups as topological groups, group schemes or pro-systems is largely a matter of choice. How is the étale homotopy group defined? …
Denis Nardin's user avatar
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15 votes

An apparent equivalence of the category of affine schemes over $S$ and the category of quasi...

What is true is that there is an antiequivalence between the category of schemes affine over $S$ (that is $S$-schemes for which the preimage of an open affine of $S$ is an open affine) and quasi-coherent …
Denis Nardin's user avatar
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10 votes

Irreducible of finite Krull dimension implies quasi-compact?

The answer is no for all these questions. Take the line with infinite origins: the scheme obtained by gluing an infinite amount of copies of $\mathbb{A}^1$ along the open subsets $\mathbb{G}_m$. This …
Denis Nardin's user avatar
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4 votes

Why geometric generic point (in abstract algebraic geometry) replace general points in the u...

If you want a canonical description of the homotopy type of the general fiber, you can take the homotopy type of the space $X\times_{\mathbb{D}}\mathbb{H}$ where $\mathbb{H}:=\{z\in\mathbb{C}\mid \Im …
Denis Nardin's user avatar
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