“…For Kleene lattices (•, ∨, ∧, * ), complexity is, to the best of the author's knowledge, an open problem. However, there are decidability results on more specific classes of Kleene lattices [3,5,37,12] (lattices in all these classes are distributive, which is not generally true for Kleene lattices), which makes it plausible that the logic of Kleene lattices is also decidable. In contrast, lattice operations are not crucial for undecidability: the logic of *-continuous residuated monoids with iteration (•, \, /, * ) is also Π 0 1 -complete [33].…”