Is an Inverse Menger Sponge a fractal?

Question

Is the Inverse of a Menger Sponge a fractal? I know a Menger sponge is fractal in nature, and it seems to me that the inverted form of it would be fractal as well, but I don't know.

Answer 1

It is not a fractal.

1. First if we consider the 2-d case(Sierpinski carpet) and the 3-d as a generalization, the precess of construction its take a square, divide it in nine squares, extract the central square and in each of the eight squares left we do the same process, now if we consider the inverse of this, it means only keep the central square and repit the process. The process in the inifinite is equal a square an object of dimention 2 then this is not a fractal. The same occurs in the case 3-d.
2. The case 3-d is not self-similar.
3. The Menger sponge is closed and its complement open then it cannot be a fractal.