Let Bpi be a family of sets, where pinmathbbN and iinI, I being a directed set, and such that, for every i, we have a descending chain of inclusions
dotssupsetBp−1isupsetBpisupsetBp+1isupsetdots
Question: is the following implication true?
bigcappBpi=emptyset,textforalliquadLongrightarrowquadbigcappvarinjlimiBpi=emptyset.
Since bigcap is a limit, this seems a problem of an interchange of limits and filtered colimits and indeed there is a universal map
varphi:varinjlimibigcappBpilongrightarrowbigcappvarinjlimiBpi
If varphi was a bijection, then my implication would be true with no doubts,
but, since the intersection is not finite, I can not say that varphi is a bijection. Nevertheless, could my implication still be true, without varphi being a bijection?
The reason behind my question is the following: let (Ai,Fi) be a directed family of filtered sets (or abelian groups, or modules; in fact, in my problem they are cochain complexes). Since filtered colimits (direct limits) are exact, you can define a filtration on the colimit like this:
FpvarinjlimiAi=varinjlimiFpiAi.
Now assume all the filtrations Fi are Hausdorff; that is, bigcappFpiAi=0 for all i. Is it then necessarily true that the filtration F on varinjlimiAi is Hausdorff too?
This question is a sequel to my previous question Convergence of right half-plane spectral sequence bounded on the right . Despite Tilman's counterexemple to my guess there, I think I've managed almost to prove it because my spectral sequences are right half-plane and this is the final detail I need.
No comments:
Post a Comment