  A language $L$ is the orthogonal catenation of languages $L_1$ and $L_2$ if
every word of $L$ can be written in a unique way as a catenation of a word in
$L_1$ and a word in $L_2$. We establish a tight bound for the state complexity
of orthogonal catenation of regular languages. The bound is smaller than the
bound for arbitrary catenation.
