CODIMENSION FORMULAE FOR THE INTERSECTION OF FRACTAL SUBSETS OF CANTOR SPACES

We examine the dimensions of the intersection of a subset E of an m-ary Cantor space C m with the image of a subset F under a random isometry with respect to a natural metric. We obtain almost sure upper bounds for the Hausdorff and upper box-counting dimensions of the intersection, and a lower bound for the essential supremum of the Hausdorff dimension. The dimensions of the intersections are typically max{dim E+dim F-dim C-m, 0}, akin to other codimension theorems. The upper estimates come from the expected sizes of coverings, whilst the lower estimate is more intricate, using martingales to define a random measure on the intersection to facilitate a potential theoretic argument.