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Assume $\Gamma$ is an infinite set composed of formulas (of finite length), and $A$ is a formula (of finite length). For example, $\Gamma=\{x,y\sqcup z,x_1,x_2,x_3,\cdots\}$, $A=(x\sqcap y)\sqcup(x\sqcap z)$. Obviously, $\mathop⨅\Gamma\le A$ holds in any of the complete distributive lattices $\langle L,\le\rangle$ (i.e. $\mathop⨅\Gamma\le A$ holds for any $x,y,z,x_1,x_2,x_3,\cdots\in L$). Meanwhile, we also can find a finite subset $\{x,y\sqcup z\}\subseteq\Gamma$ such that $\mathop⨅\{x,y\sqcup z\}\le A$ holds in any of the complete distributive lattices $\langle L,\le\rangle$ (i.e.$\mathop⨅\{x,y\sqcup z\}\le A$ holds for any $x,y,z\in L$).

Let $\mathcal{C}$ be a kind of complete lattice (with extra operations). $\mathcal{C}$ is logic-compact iff $\mathcal{C}$ satisfies the following property:

For any infinite set $\Gamma$ composed of formulas (of finite length), for any formula $A$ (of finite length), if $\mathop⨅\Gamma\le A$ holds in any instance $\mathcal{L}$ of $\mathcal{C}$, then we can always find a finite subset $\Gamma_0\subseteq\Gamma$ such that $\mathop⨅\Gamma_0\le A$ holds in any instance $\mathcal{L}$ of $\mathcal{C}$. (The operators in the formulas mentioned above contain both those in the lattice and extra equipped.)

Another example: the infinite inequality $x\sqcap(x\to y)\sqcap x_1\sqcap x_2\sqcap x_3\cdots\le y$ holds in any of the Heyting algebras, which can be attributed to the finite inequality $x\sqcap(x\to y)\le y$ holding in any of the Heyting algebras. I'm wondering whether any infinite inequality holding in any of the algebra can be attributed to a finite inequality holding in any of the algebra.

So, my question is: Does any kind of complete lattice with any operation have logic-compactness? If not, what conditions do the complete lattice and the operations need to satisfy for having the property? (e.g., bounded, distributive, etc.)

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    $\begingroup$ If the lattice is not complete, how is the definition of logic compactness involving $\bigsqcap\Gamma$ intended to be interpreted in the first place? $\endgroup$ Commented 2 days ago
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    $\begingroup$ Simultaneously cross-posted at math.stackexchange.com/questions/5115256/… . Please, do not do that. $\endgroup$ Commented 2 days ago
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    $\begingroup$ You are making the question more and more unclear. I assume “kind of lattice” just means a class $C$ of lattices, in which case the only way I can read “instance” of “this kind” is that is refers to lattices $L\in C$. But then saying “$\bigwedge\Gamma\le y$ holds for all $L\in C$” makes no sense whatsoever, as $\Gamma$, $\bigwedge\Gamma$, and $y$ only belong to one particular lattice. And you still did not clarify what happens when the meet of $\Gamma$ does not exist. $\endgroup$ Commented yesterday
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    $\begingroup$ Hmm, so the question actually asks something completely different from what it looked originally. However, it is still fairly unclear. First, “formulas” are things like $\forall x\,\exists y\,x<y$ that are either true or false; they do not evaluate in any meaningful way to elements of the lattice. It seems that when you write “formulas”, you actually mean “terms over the lattice signature”, which do indeed take values in the lattice. Certainly $y\lor z$ and $(x\land y)\lor(x\land z)$ are terms. (I’m not going to use the square symbols as they are difficult to type.) However, “$x\to y$” ... $\endgroup$ Commented yesterday
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    $\begingroup$ ... is not a term over lattices, as there is no $\to$ operation in the language of lattices. So I’m not sure what to make of that. Second, despite having been prompted for it already several times, you still haven’t explained what is supposed to happen WHEN $\bigwedge\Gamma$ DOES NOT EXIST in the lattice in question. This is absolutely crucial. For example, you claim that $\bigwedge\{x,y\lor z,x_1,x_2,x_3,\dots\}\le(x\land y)\lor(x\land z)$ holds in distributive lattices. But $(\mathbb Q,\le)$ is a distributive lattice, and when I take for $x_1,x_2,\dots$ a descending rational sequence ... $\endgroup$ Commented yesterday

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