MPI-I-94-142

We consider the problem of reporting the pairwise enclosures among a set of $n$ axes-parallel rectangles in $\IR^2$, which is equivalent to reporting dominance pairs in a set of $n$ points in $\IR^4$. For more than ten years, it has been an open problem whether these problems can be solved faster than in $O(n \log^2 n +k)$ time, where $k$ denotes the number of reported pairs. First, we give a divide-and-conquer algorithm that matches the $O(n)$ space and $O(n \log^2 n +k)$ time bounds of the algorithm of Lee and Preparata, but is simpler. Then we give another algorithm that uses $O(n)$ space and runs in $O(n \log n \log\log n + k \log\log n)$ time. For the special case where the rectangles have at most $\alpha$ different aspect ratios, we give an algorithm tha