Regularity of R(X) does not pass to finite unions
(2020)
Journal Article
Feinstein, J. F. (2020). Regularity of R(X) does not pass to finite unions. Proceedings of the American Mathematical Society, 148(7), 2931-2936. https://doi.org/10.1090/proc/14944
We show that there are compact plane sets X, Y such that R(X) and R(Y) are regular but R(X ∪ Y) is not regular.