Can a Larger Proper Filter Contain an Ultrafilter in a Boolean Algebra?

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Discussion Overview

The discussion revolves around the properties of ultrafilters within the context of Boolean algebras, specifically questioning whether a larger proper filter can exist that contains a given ultrafilter defined by the set {x in B: x>=b} for some element b in the Boolean algebra B.

Discussion Character

  • Debate/contested

Main Points Raised

  • Some participants propose that the set {x in B: x>=b} is an ultrafilter, but there is uncertainty about the existence of a larger proper filter containing it.
  • One participant questions the definition of an ultrafilter, suggesting it is a maximal proper filter, implying that no filter can contain it other than the entire Boolean algebra B.
  • Another participant suggests that a counterexample could clarify the situation and questions whether a condition, such as b being an atom, is necessary for the argument.
  • A later reply acknowledges the potential need for additional conditions, indicating that the absence of such conditions may lead to misunderstandings about the nature of ultrafilters.

Areas of Agreement / Disagreement

Participants express differing views on the existence of a larger proper filter containing the ultrafilter, with some suggesting that additional conditions are necessary for clarity. The discussion remains unresolved regarding the implications of these conditions.

Contextual Notes

There is a noted limitation regarding the assumption that b is an atom, which may affect the validity of the claims about ultrafilters and filters in Boolean algebras.

quasar987
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Let B be a boolean algebra with smaller element 0, and let b different from 0 be in B. Apparently, {x in B: x>=b} is an ultrafilter of B.

I don't understand why a priori there could not exists a larger proper filter containing this one!
 
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I'm not sure what you you mean by that question.
 
Well, an ultrafilter in a boolean algebra (B,u,n,C,0,1) is as far as I understand, a proper filter that is maximal, in the sense that there are no filter containing it other than B itself.

Why is the set {x in B: x>=b} from post #1 an ultrafilter. Why can't there be a filter containing it other than B?
 
Have you tried constructing a counterexample?



Anyways, are you sure you're not missing a condition? e.g. is b supposed to be an atom?
 
I had vaguely found a counterexample, that's why I asked the question. Now it's clear that a condition such as "b is an atom" is missing. Thanks.
 

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