### A characterization of distributive lattices by tolerance lattices

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The concept of a deductive system has been intensively studied in algebraic logic, per se and in connection with various types of filters. In this paper we introduce an axiomatization which shows how several resembling theorems that had been separately proved for various algebras of logic can be given unique proofs within this axiomatic framework. We thus recapture theorems already known in the literature, as well as new ones. As a by-product we introduce the class of pre-BCK algebras.

We characterize ideals of ortholattices which are congruence kernels. We show that every congruence class determines a kernel.

To each indefinite integral binary quadratic form $Q$, we may associate the geodesic in $\mathbb{H}$ through the roots of quadratic equation $Q(x,1)$. In this paper we study the asymptotic distribution (as discriminant tends to infinity) of the angles between these geodesics and one fixed vertical geodesic which intersects all of them.