#17096: Implement categories for filtered algebras
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       Reporter:  tscrim             |        Owner:  tscrim
           Type:  enhancement        |       Status:  needs_review
       Priority:  major              |    Milestone:  sage-6.4
      Component:  categories         |   Resolution:
       Keywords:  filtered algebras  |    Merged in:
        Authors:  Travis Scrimshaw   |    Reviewers:
Report Upstream:  N/A                |  Work issues:
         Branch:                     |       Commit:
  public/categories/filtered_algebras-17096|  
b29f67e46e18721313330d3a6e116cf3df2eaf8e
   Dependencies:                     |     Stopgaps:
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Comment (by jhpalmieri):

 A few questions and comments:

 - in `filtered_modules.py`, it talks about modules over a commutative
 ring, but the word "commutative" can be deleted, I think.
 - in the same file, it says
 {{{
 .. TODO::

     Implement a notion for decreasing filtrations: where `F_j \subseteq
 F_i`.
 }}}
  If you want to keep this remark, then you should add "when i \leq j". But
 do you need to keep this? If you want a decreasing filtration, just use
 the non-positive integers for your indexing set instead of non-negative
 integers. For example, if you have an algebra `A` and an ideal `I`, then
 you can set `F_{-n}A` equal to the `n`th power of `I`. Then you have `F_0
 \supseteq F_{-1} \supseteq F_{-2} \supseteq ...`: a decreasing filtration.
 - How could we implement an algebra which is both graded and filtered?
 This is the situation for the Steenrod algebra, for example.

--
Ticket URL: <http://trac.sagemath.org/ticket/17096#comment:35>
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