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The study of algebraic structures and properties applying to large classes of such structures. For example, ideas from group theory and ring theory are extended and considered for structures with other signatures (systems of basic or fundamental operations).

3 votes
1 answer
206 views

Join prime pseudovarieties

A pseudovariety $\mathbf{V}$ of groups is join prime if for any pseudovarieties $\mathbf{V}_1, \mathbf{V}_2, \ldots,\mathbf{V}_m$, the implication $$\mathbf{V} \subseteq \mathbf{V}_1 \vee \mathbf{V}_2 …
8 votes
0 answers
199 views

Varieties of groups with certain properties

Is there an example of a periodic variety $\mathbf{V}$ of groups that satisfies all of the following properties? $\mathbf{V}$ is finitely based $\mathbf{V}$ contains finitely many subvarieties $\mat …
3 votes

Example of a non-finitely based variety with explicit set of defining identities

There are a few examples that are finitely generated. (1) Let $L$ be Lyndon's groupoid given by the following multiplication table: \begin{array} [c]{c|ccccccc} L & 0 & 1 & 2 & 3 & 4 & 5 & 6 \\ \hl …
E W H Lee's user avatar
  • 563
5 votes
0 answers
137 views

Pseudovarieties of monoids

All (pseudo)varieties considered here are (pseudo)varieties of monoids. It is known that any (finite or infinite) monoid that satisfies the identities \begin{equation} xhxyty = xhyxty, \quad xhytxy=x …
5 votes

Locally finite varieties which are not finitely generated

Many small semigroups generate varieties that contain non-finitely generated subvarieties. For instance, the 3-element semigroup $\langle a,1\,|\,a^2=0\rangle$ and the 4-element semigroup $\langle a,b …
E W H Lee's user avatar
  • 563
3 votes
0 answers
140 views

Non-finitely based varieties and pseudovarieties

The variety of semigroups defined by $B=\Big\{(x^py^p)^2=(y^px^p)^2:p \text{ is prime}\Big\}$ is non-finitely based (Isbell, 1970). Is the pseudovariety defined by $B$ also non-finitely based? More g …