  We examine non-dual relational extensions of rough set approximations and
find an extension which satisfies surprisingly many of the usual rough set
properties. We then use this definition to give an explanation for an
observation made by Samanta and Chakraborty in their recent paper [P. Samanta
and M.K. Chakraborty. Interface of rough set systems and modal logics: A
survey. Transactions on Rough Sets XIX, pages 114-137, 2015].
