Varieties whose tolerances are homomorphic images of their congruences

The homomorphic image of a congruence is always a tolerance (relation) but, within a given variety, a tolerance is not necessarily obtained this way. By a Maltsev-like condition, we characterize varieties whose tolerances are homomorphic images of their congruences (TImC). As corollaries, we prove that the variety of semilattices, all varieties of lattices, and all varieties of unary algebras have TImC. We show that a congruence n-permutable variety has TImC if and only if it is congruence permutable, and construct an idempotent variety with a majority term that fails TImC

On tractability and congruence distributivity

Constraint languages that arise from finite algebras have recently been the object of study, especially in connection with the Dichotomy Conjecture of Feder and Vardi. An important class of algebras are those that generate congruence distributive varieties and included among this class are lattices, and more generally, those algebras that have near-unanimity term operations. An algebra will generate a congruence distributive variety if and only if it has a sequence of ternary term operations, called Jonsson terms, that satisfy certain equations. We prove that constraint languages consisting of relations that are invariant under a short sequence of Jonsson terms are tractable by showing that such languages have bounded relational width

Szikesvizek mezo- és makrofauna együttesei, populációméretek és táplálkozási kapcsolatok a vízimadarak felé = Aquatic invertebrate assemblages in sodic waters, population sizes and feeding connection to the aquatic birds

2002-ben, 2003-ban a HNP, a KNP és FHNP szikes vizeiben végeztünk zooplankton és gerinctelen makrofauna vizsgálatokat azzal a céllal, hogy felmérjük a parkok Európa szerte méltán híres vízimadár populációk számára rendelkezésre álló táplálékkínálatot. Összesen 15 kisrákfaj (9 Cladocera és 6 Copepoda) került elő a 85um-es hálóval való szürés során. A rákok denzitása 4-2728 ind/l között, szélsőségesen változott. Ezek a fajok a különféle uszórécék, különösen a kanalas, tőkés és a csörgőrécék számára nyújtanak jó táplálékforrást. A bentonikus állatok közül a hemimetabol szervezeteket csak szórványosan találtuk a bentoszban. A fehér szikesek fenékfaunája az újabb felméréseink szerint is rendkívül szegényesnek adódott. Az iszapban csak gyűjtésenként egy-két árva és törpeszúnyogot valamint gyűrűsférget találtunk. A fertői elárasztott tavak szélirányos részénél (koncentrált táplálkozóhely) a hullámzáshoz kapcsolódó ökológiai tényezők hatnak kiemelkedően. | The sodic ponds are the world famous remnants of ancient wetland in the Carpathian Basin. The aim of this study is to estimate the population sizes of waterfowl in the small sodic ponds, and to complete our knowledge about the feeding parameters of water birds or their regulation effects for the material cycle in the continental sodic waters. In the water, the biomass and the production of the algae are relatively low. The species number and density of the zooplankton are very variable in time and space and the characteristic. In white, sodic waters, only a few Oligochaeta, Chironomida and Ceratopogonida can be found. Parallel with the potential and the real food supply examinations, the guild groups of aquatic birds also studied. We divided them into three guild groups the aquatic bird species. These were the transporters, the accelerators and bioturbation accelerates. From the territories, 115 aquatic bird species were found. 15 species of material transporters, mainly the grazer geese (41 ind/ha density). The dabbling ducks and the Coot's max. individual number was 50601 (density 68 ind/ha). In the white sodic ponds, analysis of alimentary canals of birds and feeding experiments showed that the regulations of organic material and energy cycle in these waters instead of the 'bottom-up' regulation, the important. In these waters, the roles of the fishes missing replace by the nourishment, defecations and mechanical effects of the aquatic bird guilds