We have seen that a non-commutative
algebra
finite dimensional
extension of
the algebras
Grothendieck-topology on
and let
Galois group. Consider the
category with objects the finite
sets with an action of
set-maps, that is: maps respecting the group action. For each object
cover of
of
this is an example of a Grothendieck-topology as it satisfies
the following three conditions :
(GT1) : If
(GT2) : If
is in
(GT3) : If
and
products
again a
is in
Now, finite
commutative separable
commutative
finite
stabilizer subgroup of an element in
index in
separable field extension of
corresponds uniquely to a separable
finite cover
that
the Grothendieck topology of finite
is anti-equivalent to the category of commutative separable
This raises the natural question : what happens if we extend the
category to all separable
non-commutative
Grothendieck topology? Or do we get something like a
non-commutative Grothendieck topology as defined by Fred Van
Oystaeyen (essentially replacing the axiom (GT 3) by a left and right
version). And if so, what are the non-commutative covers?
Clearly, if
these non-commutative covers to be the set of all separable
that is, if