“…Other arithmetic operations with x, y ∈ K are considered in [2], which describes the structure of quotients y/x with x = 0 and proves that [0, 1] is covered by products x 2 y, so that in particular any element of [0, 1] is the product of 3 factors in K. In [5] it is proved that sums x 2 1 + x 2 2 + x 2 3 + x 2 4 with x i ∈ K for i = 1, 2, 3, 4 cover [0, 4], which was conjectured in [2]. In [6] is described a general condition on maps f : R 2 → R such that f (K × K) has non-empty interior, where such condition is obviously satisfied by the arithmetic operation mentioned above. For the image under affine maps, and in particular for S(x, y) := x + y, a much larger class of Cantor sets and other fractals have been studied.…”