%0 Journal Article %T Characterisations of Nelson algebras %A Spinks %A M. %A Veroff %A R. %J Revista de la Uni£¿3n Matem£¿£¿tica Argentina %D 2007 %I Uni¨®n Matem¨¢tica Argentina %X nelson algebras arise naturally in algebraic logic as the algebraic models of nelson's constructive logic with strong negation. this note gives two characterisations of the variety of nelson algebras up to term equivalence, together with a characterisation of the finite nelson algebras up to polynomial equivalence. the results answer a question of blok and pigozzi and clarify some earlier work of brignole and monteiro. %K nelson algebra %K residuated lattice %K bck-algebra %K equationally definable principal congruences. %U http://www.scielo.org.ar/scielo.php?script=sci_abstract&pid=S0041-69322007000100004&lng=en&nrm=iso&tlng=en