$c_{0} \widehat{\otimes}_πc_{0}\widehat{\otimes}_πc_{0}$ is not isomorphic to a subspace of $c_{0} \widehat{\otimes}_πc_{0}$
Ryan M. Causey, Elói Medina Galego, Christian Samuel · arXiv (Cornell University) · 2020
In the present paper we prove that the $3$-fold projective tensor product of $c_0$, $c_{0} \widehat{\otimes}_πc_{0}\widehat{\otimes}_πc_{0}$, is not isomorphic to a subspace of $c_{0} \widehat{\otimes}_πc_{0}$. In particular, this settles the long-standing open problem of whether $c_{0} \widehat{\otimes}_πc_{0}$ is isomorphic to $c_{0} \widehat{\otimes}_πc_{0}\widehat{\otimes}_πc_{0}$. The origin of this problem goes back to Joe Diestel who mentioned it in a private communication to the authors of paper "Unexpected subspaces of tensor products" published in 2006.