The following might be a somewhat esoteric question:
Does there exist an infinite cardinal $\kappa$ and a section $f$ of the quotient map $\pi:\mathcal{P}(\kappa)\to\mathcal{P}(\kappa)/(\text{fin})$ (i.e., $f:\mathcal{P}(\kappa)/(\text{fin})\to\mathcal{P}(\kappa)$ and $\pi\circ f=\text{Id}_{\mathcal{P}(\kappa)/(\text{fin})}$) s.t.,
- $f$ is monotone;
- If $x_1,\cdots,x_n\in\mathcal{P}(\kappa)/(\text{fin})$ are such that $\bigvee_{i=1}^nx_i=[\kappa]$, then $\bigcup_{i=1}^nf(x_i)=\kappa$;
- For any ultrafilter $\mathcal{U}$ on $\mathcal{P}(\kappa)/(\text{fin})$, $\bigcap_{x\in\mathcal{U}}f(x)=\varnothing$.
If this is not possible, what if $\mathcal{P}(\kappa)/(\text{fin})$ is replaced by a further (Boolean algebra) quotient? (That will already be enough for my purposes.)
This is related to my attempt at a topology question. One of my approaches at constructing a counterexample for that question requires the existence of a section $f$ as above. (The precise connection is not really relevant to the present question.) It is not immediately clear to me that such an $f$ should not exist - I'm aware that if $f$ is required to be a Boolean algebra homomorphism, this is probably impossible (at least when $\kappa=\omega$), but conditions $1$ and $2$ are a priori strictly weaker than asking for a Boolean algebra homomorphism.