Paper detail

Adjoint operations in twist-products of lattices

Given an integral commutative residuated lattice L=(L,\vee,\wedge), its full twist-product (L^2,\sqcup,\sqcap) can be endowed with two binary operations \odot and \Rightarrow introduced formerly by M. Busaniche and R. Cignoli as well as by C. Tsinakis and A. M. Wille such that it becomes a commutative residuated lattice. For every a in L we define a certain subset P_a(L) of L^2. We characterize when P_a(L) is a sublattice of the full twist-product (L^2,\sqcup,\sqcap). In this case P_a(L) together with some natural antitone involution ' becomes a pseudo-Kleene lattice. If L is distributive then (P_a(L),\sqcup,\sqcap,') becomes a Kleene lattice. We present sufficient conditions for P_a(L) being a subalgebra of (L^2,\sqcup,\sqcap,\odot,\Rightarrow) and thus for \odot and \Rightarrow being a pair of adjoint operations on P_a(L). Finally, we introduce another pair \odot and \Rightarrow of adjoint operations on the full twist-product of a bounded commutative residuated lattice such that the resulting algebra is a bounded commutative residuated lattice satisfying the double negation law and we investigate when P_a(L) is closed under these new operations \odot and \Rightarrow.