The realization of this monograph has needed some permissions to use copyrighted material. Hence I would like to thank Springer (chapters 6, 7, 8 are derived from papers [ABM09a, BM09, BM10]) and Professors S. Burris and H.P. Sankappanavar (some of the figures in the appendix are taken from the electronic version of their book [BS81]) to have granted their permissions. I profit also to thank Pr...

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Using -congruences and implications, Weaver (1993) introduced the concepts of prevariety and quasivariety of first-order structures as generalizations of the corresponding concepts for algebras. The notion of functional completeness on algebras has been defined and characterized by Burris and Sankappanavar (1981), Kaarli and Pixley (2001), Pixley (1996), and Quackenbush (1981). We study the not...

In [4, Definition 8.1], some important subvarieties of the variety SH of semi-Heyting algebras are defined. The purpose of this paper is to introduce and investigate the subvariety ISSH of SH, characterized by the identity (0  1)  (0  1)  1. We prove that ISSH contains all the subvarieties introduced by Sankappanavar and it is in fact the least subvariety of SH with this property. We als...

Semi De Morgan algebras form a variety of normal distributive lattice expansions [7] introduced by H.P. Sankappanavar [16] as a common abstraction of De Morgan algebras and distributive pseudocomplemented lattices. A fully selfextensional logic SDM naturally arises from semi De Morgan algebras, which has been studied from a duality-theoretic perspective [13], from the perspective of canonical e...

There is a well known interplay between the study of algebraic varieties and propositional calculus of various logics. Prime examples of this are boolean algebras and classical logic, and Heyting algebras and intuitionistic logic. After the class of Heyting algebras was generalized to the semi-Heyting algebras by H. Sankappanavar in [San08], its logic counterpart was developed by one of us in [...

In this study, the relationship among four species of Polygonum (including P. hyrcanicum (three samples), P. persicaria, P. avicular, and P. hydropiper) was investigated by GC profiling. Furthermore, the major compounds of the ethylic ether extract of P. hyrcanicum were identified by GC/MS as: α-bisabolol (17.5%), cedrol (15.9%), sesquisabinene hydra...