Ball generated property of direct sums of Banach spaces

A Banach space $X$ is said to have the ball generated property (BGP) if every closed, bounded, convex subset of $X$ can be written as an intersection of finite unions of closed balls. In 2002 S. Basu proved that the BGP is stable under (infinite) $c_0$- and ${\mathrm{\ell }}^p$-sums for $1<p<\mathrm{\infty }$. We will show here that for any absolute, normalised norm $\mathrm{\parallel }\cdot {\mathrm{\parallel }}_E$ on ${\mathbb{R}}^2$ satisfying a certain smoothness condition the direct sum $X{\oplus }_{E}Y$ of two Banach spaces $X$ and $Y$ with respect to $\mathrm{\parallel }\cdot {\mathrm{\parallel }}_E$ enjoys the BGP whenever $X$ and $Y$ have the BGP.