Graph isomorphic discrete partially ordered sets and semimodularity

In [RATANAPRASERT, C.—DAVEY, B.: Semimodular lattices with isomorphic graphs, Order 4 (1987), 1–13], the authors found conditions under which an isomorphism of graphs of discrete lattices transfers semimodularity. The main theorem of the present paper generalizes their result for discrete partially ordered sets.     

Generalized Specker lattice-ordered groups and two types of distributivity

Let A be a lattice-ordered group, B a generalized Boolean algebra. The Boolean extension A _B of A has been investigated in the literature; we will refer to A _B as a generalized Specker lattice-ordered group (namely, if A is the linearly ordered group of all integers, then A _B is a Specker lattice-ordered group). The paper establishes that some distributivity laws extend from A _B to both A and B, and (under certain circumstances) also conversely.     

The equality problem in the class of conjugate means

Let ${I\subset\mathbb{R}}$ be a nonempty open interval and let ${L:I^2\to I}$ be a fixed strict mean. A function ${M:I^2\to I}$ is said to be an L-conjugate mean on I if there exist ${p,q\in{]}0,1]}$ and a strictly monotone and continuous function φ such that $$M(x,y):=\varphi^{-1}(p\varphi(x)+q\varphi(y)+(1-p-q)\varphi(L(x,y)))=:L_\varphi^{(p,q)}(x,y),$$ for all ${x,y\in I}$ . Here L(x, y) is a fixed quasi-arithmetic mean. We will solve the equality problem in this class of means.     

Varieties of Posets

We introduce and investigate the notion of a homomorphism, of a congruence relation, of a substructure of a poset and consequently the notion of a variety of posets. These notions are consistent with those used in lattice theory and multilattice theory. There are given some properties of the lattice of all varieties of posets.