Storing four elements in the two query bitprobe model

In this paper, we look into the adaptive bitprobe model that stores subsets of size at most four from a universe of size m, and answers membership queries using two bitprobes. We propose a scheme that stores arbitrary subsets of size four using O(m(4/5)) amount of space. This improves upon the O(m(5/6))-scheme by the authors Baig et al. (2019). The proposed scheme also answers an open problem posed by Nicholson (2019) in the affirmative. (c) 2021 Elsevier B.V. All rights reserved.