The class of 2-dimensional neat reducts is not elementary
Tom 172 / 2002
Fundamenta Mathematicae 172 (2002), 61-81
MSC: Primary 03G15; Secondary 06E25, 08B99.
DOI: 10.4064/fm172-1-5
Streszczenie
$SC$, $CA$, $QA$ and $QEA$ stand for the classes of Pinter's substitution algebras, Tarski's cylindric algebras, Halmos' quasipolyadic algebras and Halmos' quasipolyadic algebras with equality, respectively. Generalizing a result of Andréka and Németi on cylindric algebras, we show that for $K\in \{SC,QA,CA,QEA\}$ and any $\beta >2$ the class of $2$-dimensional neat reducts of $\beta $-dimensional algebras in $K$ is not closed under forming elementary subalgebras, hence is not elementary. Whether this result extends to higher dimensions is open.
