Is there existing terminology for this technical condition on semilattices?

2011-12-10T05:32:23Z

Given a semilattice $S$, a subset $E$, and a positive integer $n$, let $E^{[n]}$ be the set of all products of $n$-tuples in $E$. Thus $\bigcup_{n\geq 1} E^{[n]}$ is nothing but the subsemigroup of $S$ generated by $E$, which I'll denote by $\langle E\rangle$.

The following definition arose in some work I am writing up, as a technical condition needed to make a theorem work.

Definition. $S$ has "generation depth $\leq n$" if there exists $n$ such that $E^{[n]} = \langle E\rangle$ for every subset $E\subseteq S$.

The terminology is my own, because I don't know if there is existing terminology that I should be using instead. So my questions are: has anyone seen this definition before, and do they have a reference where this condition is given an explicit name?

Some remarks. It is clear that for each $n$, I can find a finite semilattice which does not have generation depth $\leq n$ (a free semilattice on at least $n+1$ generators, for instance). On the other hand, easy pigeon-hole arguments show that a semilattice of width $n$ has generation depth $\leq n$, as does a semilattice of height $n$.

UPDATE Some more context, in case it helps or is suggestive. The condition arises from the following question:

Given a semilattice $S$ and a weight $\omega$ on $S$, that is to say, a submultiplicative function $\omega: S \to [1,\infty)$, suppose $\psi:S \to {\mathbb C}$ is approximately multiplicative, in the sense that $$ \sup_{x,y\in S} \omega(x)^{-1}\omega(y)^{-1} |\psi(x)\psi(y)-\psi(xy)| \hbox{ is small.} $$ Does this force $\psi$ to be a small perturbation of a multiplicative function $S\to\{0,1\}$ ?

It turns out that the answer is YES if $S$ has "generation depth $\leq n$" for some $n$, regardless of the choice of $\omega$ -- roughly speaking, if I know what $\psi$ does on some subset $E$, then the condition allows me to control what $\psi$ does on the filter generated by $E$.
As a partial converse, I can find a semilattice $S$ and a weight $\omega$ such that the answer is NO (the counter-example is what motivated the definition).

Answer by NN for Is there existing terminology for this technical condition on semilattices?

2012-06-29T19:05:26Z

in lattice theoretic terms, the condition is "finite breadth" (more on this in the comment above and with search engine requests for "breadth lattice")

Is there existing terminology for this technical condition on semilattices? - MathOverflow

Is there existing terminology for this technical condition on semilattices?

Answer by NN for Is there existing terminology for this technical condition on semilattices?