**Abstract.** The history of productivity of the $\kappa$-chain condition in partial orders, topological spaces, or Boolean algebras is surveyed, and its connection to the set-theoretic notion of a weakly compact cardinal is highlighted. Then, it is proved that for every regular cardinal $\kappa>\aleph_1$, the principle $\square(\kappa)$ is equivalent to the existence of a certain strong coloring $c:[\kappa]^2\rightarrow\kappa$ for which the family of fibers $\mathcal T(c)$ is a nonspecial $\kappa$-Aronszajn tree.

The theorem follows from an analysis of a new characteristic function for walks on ordinals, and implies in particular that if the $\kappa$-chain condition is productive for a given regular cardinal $\kappa>\aleph_1$, then $\kappa$ is weakly compact in some inner model of ZFC. This provides a partial converse to the fact that if $\kappa$ is a weakly compact cardinal, then the $\kappa$-chain condition is productive.

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**Citation information:**

A. Rinot, *Chain conditions of products, and weakly compact cardinals*, Bull. Symbolic Logic, 20(3): 293-314, 2014.

Is it known if for inaccessible $\kappa, \square(\kappa)+GCH$ implies the existence of a $\kappa-$Souslin tree?

I was thinking maybe your new characterization of $\square(\kappa)$ can be used to discuss this problem.

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