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10 votes

Grothendieck Topologies versus Pretopologies

A Grothendieck topology by definition consists of sieves – what Johnstone calls a sifted coverage – whereas a Grothendieck pretopology in any non-trivial case will contain a non-sieve. (Recall that $\ …
Zhen Lin's user avatar
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17 votes
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Definition of ind-schemes

There is in fact no difference between the two definitions if you take your site to be the category of affine schemes – while it is true that the forgetful functor from sheaves to presheaves does not preserve …
Zhen Lin's user avatar
  • 15.9k