Among the orbit patterns that force only eventually fixed trajectories, we completely describe the forcing relation, by answering the question: which orbit patterns force which others? (for details see [7])). In another [2] it is the language of locating periodic points of period 1 and 2. In yet another [6], it is an index set for the set of orbit-patterns.
Statement of Main Result.There is a natural bijection between the language {L, R} * and the set of all EF orbit patterns. The forcing relation on the latter set receives a neat description when framed in the terminology of theory of languages. We are able to find four rules of derivation in {L, R} * so that the following theorem becomes true: An orbit pattern α forces another orbit pattern β if and only if the corresponding word of β can be derived from that of α using four rules of derivation (described below).