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Recall that if $M,N$ are two structures of the same type, then $M$ is $\mathcal{L}_{\infty,\omega}$ elementarily equivalent to $N$ precisely when $M$ and $N$ are isomorphic in some forcing extension. Furthermore, as Joel David Hamkins has observed, if $M,N$ are $\mathcal{L}_{\infty,\omega}$ elementarily equivalent and $V[G]$ is a forcing extension that collapses $|M|,|N|$ to $\aleph_{0}$, then $M,N$ become isomorphic in $V[G]$. I am wondering if there is a topological version of this result.

A frame is a complete lattice $L$ that satisfies the infinite distributivity identity $$x\wedge\bigvee_{i\in I}y_{i}=\bigvee_{i\in I}(x\wedge y_{i}).$$ A frame homomorphism is a mapping $\phi:L\rightarrow M$ that preserves finite meets, arbitrary joins, and $0,1$. If $(X,\mathcal{T})$ is a topological space, then $\mathcal{T}$ is always a frame. Frames are the central object of study in point-free topology since all of the information in a good space $(X,\mathcal{T})$ is contained in the lattice $\mathcal{T}$. Most notions from general topology immediately generalize seamlessly the point-free topology. One is referred to the book “Frames and Locales: Topology without points” for an exposition on point-free topology.

Suppose that $L$ is a completely regular frame and $B$ is a complete Boolean algebra. Then let $L^{+B}$ be the set of all frame homomorphisms $\phi:L\rightarrow B$. Then set $\|\phi=\theta\|\geq b$ precisely when $\phi(x)\wedge b=\theta(x)\wedge b$ for all $x\in X$. Then $L^{+B}$ is a complete $B$-valued set. $L^{+B}$ becomes a $B$-valued topological space with $B$-valued basis consisting of all systems $\sum_{b\in p}\underline{x_{b}}\cdot b$ where $p$ is a partition of $B$, $x_{b}\in L$ for $b\in p$, and where $\|\phi\in\sum_{b\in p}\underline{x_{b}}\cdot b\|=\bigvee_{b\in p}(\phi(x_{b})\wedge b)\|.$

Suppose $L,M$ are completely regular frames. Then does there exist some logic $\mathcal{L}$ where $L$ and $M$ are $\mathcal{L}$-elementarily equivalent precisely when there is some complete Boolean algebra $B$ such that for all complete Boolean algebras $C$ with $B\subseteq C$ and where $B$ is a complete subalgebra of $C$ we have $$V^{C}\models\text{$L^{+C}$ and $M^{+C}$ are homeomorphic}?$$ Does there exist a version of this result for uniform frames of for complete uniform frames?

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    $\begingroup$ One might mention that in the structure case, two structures are forceably isomorphic if and only if they are isomorphic in the forcing extension in which they both become countable. So one doesn't need to guess which forcing notion might do it. Another thing is that there is also a game-theoretic characterization: structures $A$ and $B$ are isomorphic in a forcing extension if and only if player II has a winning strategy in the game to build a partial isomorphism (like a pebble game), where player I challenges with new points in the domain or range and player II plays corresponding points. $\endgroup$ Commented Nov 25, 2017 at 20:42
  • $\begingroup$ What do you mean by "frame" in this question? $\endgroup$ Commented Nov 25, 2017 at 20:42
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    $\begingroup$ A frame is a complete lattice in which finite meets distribute over arbitrary joins. A morphism of frames is a poset map map that preserves finite meets and arbitrary joins. $\endgroup$ Commented Nov 25, 2017 at 20:57

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