[For the entire collection see Zbl 0604.00016.] If $h: X\sp*\to Y\sp*$ is a non-trivial k-free morphism then (except a rather technical possibility for $k=3)$ h is a primitive ps-code. All k- free morphisms are characterized in case $k\ge q\sb h+1$ and for a class of morphisms in the case $2\le k\le q\sb h$, where $q\sb h=\max \{\vert h(a)\vert$, $a\in X\}$.
Reviewer: Ja.Henno