Sequential Separability Vs Selective Sequential Separability

Angelo Bella, Camillo Costantini

A space $X$ is sequentially separable if there is a countable $D\subset X$ such that every point of $X$ is the limit of a sequence of points from $D$. We present two examples of a sequentially separable space which is not selectively sequentially separable. One of them is in addition countable and sequential.