pretopology
Noun
Meaning
(mathematics) The field of study of pretopological spaces (in plural for different prespaces).
(mathematics) A filter subset or a preclosure operator which acts as a distinct prespace (pre-topological space).
Source: en.wiktionary.orgExamples
If J is the topology defined by a pretopology, and if u commutes with fibered products, then u is continuous if and only if it sends covering sieves to covering sieves and if and only if it sends covering families to covering families.
The Zariski topology on Sch is generated by the pretopology whose covering families are jointly surjective families of scheme-theoretic open immersions.
The indiscrete topology is also known as the biggest or chaotic topology, and it is generated by the pretopology which has only isomorphisms for covering families.
If the collection of all covering families satisfies certain axioms, then we say that they form a Grothendieck pretopology.
We can also define this topology using the same pretopology we used above.