  In the present paper we prove that the $3$-fold projective tensor product of
$c_0$, $c_{0} \widehat{\otimes}_\pi c_{0}\widehat{\otimes}_\pi c_{0}$, is not
isomorphic to a subspace of $c_{0} \widehat{\otimes}_\pi c_{0}$. In particular,
this settles the long-standing open problem of whether $c_{0}
\widehat{\otimes}_\pi c_{0}$ is isomorphic to $c_{0} \widehat{\otimes}_\pi
c_{0}\widehat{\otimes}_\pi c_{0}$. 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.
