Abstract:

If element $z$ of a lattice effect algebra $(E,\oplus, {\mathbf 0}, {\mathbf 1})$ is central, then the interval $[{\mathbf 0},z]$ is a lattice effect algebra with the new top element $z$ and with inherited partial binary operation $\oplus$. It is a known fact that if the set $C(E)$ of central elements of $E$ is an atomic Boolean algebra and the supremum of all atoms of $C(E)$ in $E$ equals to the top element of $E$, then $E$ is isomorphic to a direct product of irreducible effect algebras (\cite{R2}). In \cite{PR} Paseka and Riečanová published as open problem whether $C(E)$ is a bifull sublattice of an Archimedean atomic lattice effect algebra $E$. We show that there exists a lattice effect algebra $(E,\oplus, {\mathbf 0}, {\mathbf 1})$ with atomic $C(E)$ which is not a bifull sublattice of $E$. Moreover, we show that also $B(E)$, the center of compatibility, may not be a bifull sublattice of $E$.