Simultaneous translational and multiplicative tiling and wavelet sets in ℝ²

Simultaneous tiling for several different translational sets has been studied rather extensively, particularly in connection with the Steinhaus problem. The study of orthonormal wavelets in recent years, particularly for arbitrary dilation matrices, has led to the study of multiplicative tilings by the powers of a matrix. In this paper we consider the following simultaneous tiling problem: Given a lattice in ℒ ∈ ℝ^d and a matrix A ∈ GL (d, ℝ), does there exist a measurable set T such that both {T + α : α ∈ ℒ} and {AⁿT : n ∈ ℤ} are tilings of ℝ^d? This problem comes directly from the study of wavelets and wavelet sets. Such a T is known to exist if A is expanding. When A is not expanding the problem becomes much more subtle. Speegle [24] exhibited examples in which such a T exists for some ℒ and nonexpanding A in ℝ². In this paper we give a complete solution to this problem in ℝ². Indiana University Mathematics Journal