In this paper we consider the relationship between the Assouad and
box-counting dimension and how both behave under the operation of taking
products. We introduce the notion of `equi-homogeneity' of a set, which
requires a uniformity in the size of local covers at all lengths and at all
points. We prove that the Assouad and box-counting dimensions coincide for sets
that have equal upper and lower box-counting dimensions provided that the set
`attains' these dimensions (analogous to `s-sets' when considering the
Hausdorff dimension), and the set is equi-homogeneous. Using this fact we show
that for any $\alpha\in(0,1)$ and any $\beta,\gamma\in(0,1)$ such that $\beta +
\gamma\geq 1$ we can construct two generalised Cantor sets $C$ and $D$ such
that $\text{dim}_{B}C=\alpha\beta$, $\text{dim}_{B}D=\alpha\gamma$, and
$\text{dim}_{A}C=\text{dim}_{A}D=\text{dim}_{A}(C\times
D)=\text{dim}_{B}(C\times D)=\alpha$
We show that self-similar sets arising from iterated function systems that satisfy the Moran open-set condition, a canonical class of fractal sets, are 'equi-homogeneous'. This is a regularity property that, roughly speaking, means that at each fixed length-scale any two neighbourhoods of the set have covers of approximately equal cardinality.Self-similar sets are notable in that they are Ahlfors-David regular, which implies that their Assouad and box-counting dimensions coincide. More generally, attractors of non-autonomous iterated functions systems (where maps are allowed to vary between iterations) can have distinct Assouad and box-counting dimensions. Consequently the familiar notion of Ahlfors-David regularity is too strong to be useful in the analysis of this important class of sets, which include generalised Cantor sets and possess different dimensional behaviour at different length-scales. * EJO was partially supported by EPSRC grant EP/G007470/1 while at Warwick on sabbatical leave from University of Nevada Reno.† JCR was partially supported by an EPSRC Leadership Fellowship, grant EP/G007470/1. ‡ NS was partially supported by an EPSRC Career Acceleration Fellowship, grant EP/I004165/1, awarded to Martin Rasmussen, whose support is gratefully acknowledged.We further develop the theory of equi-homogeneity showing that it is a weaker property than Ahlfors-David regularity and distinct from any previously defined notion of dimensional equivalence. However, we show that if the upper and lower box-counting dimensions of an equi-homogeneous set are equal and 'attained' in a sense we make precise then the lower Assouad, Hausdorff, packing, lower box-counting, upper box-counting and Assouad dimensions coincide.Our main results provide conditions under which the attractor of a non-autonomous iterated function system is equi-homogeneous and we use this to compute the Assouad dimension of a certain class of these highly non-trivial sets.
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