  It is known that a best low-rank approximation to multi-way arrays or
higher-order tensors may not exist. This is due to the fact that the set of
multi-way arrays with rank at most $R$ is not closed. Nonexistence of the best
low-rank approximation results in diverging rank-1 components when an attempt
is made to compute the approximation. Recently, a solution to this problem has
been proposed for real $I\times J\times 2$ arrays. Instead of a best rank-$R$
approximation the best fitting Generalized Schur Decomposition (GSD) is
computed. Under the restriction of nonsingular upper triangular matrices in the
GSD, the set of GSD solutions equals the interior and boundary of the rank-$R$
set. Here, we show that this holds even without the restriction. We provide a
complete classification of interior, boundary, and exterior points of the
rank-$R$ set of real $I\times J\times 2$ arrays, and show that the set of GSD
solutions equals the interior and boundary of this set.
