  The determination of the maximal ranks of a set of a given type of tensors is
a basic problem both in theory and application. In statistical applications,
the maximal rank is related to the number of necessary parameters to be built
in a tensor model. Based on this classical theorem by Bosch we will show the
tight bound for 2 x n x n tensors by simple row and column operations,
symmetrization and mathematical induction, which has been given by several
authors based on eigenvalue theories.
