Complemented subspaces of $J$-sums of Banach spaces

Abstract

We study the complemented subspaces of the $J$-sums of Banach spaces $J(\Phi)$ and $\hat J(\Phi)$ introduced by Bellenot. As an application, we show that, under some conditions, $J(\Phi)$ and $\hat J(\Phi)$ are subprojective, i.e., every closed infinite-dimensional subspace of either of them contains a complemented infinite-dimensional subspace.