One of the DP transformations is narrowing:
an SCC consisting of pairs P ∪ { s → t } over a set of rules R can be narrowed to
P ∪ {sμ1 → t1, ..., sμn → tn}
iff
(termination case)
t1, ..., tn are all R-narrowings of t with the mgu's μ1,
..., μn and t does not unify with left-hand sides of pairs in P. Moreover, P
must be linear.
(innermost termination case)
t1, ..., tn are all R-narrowings of t with the mgu's μ1,
..., μn such that sμi is in R-normal form. Moreover, for all v → w ∈ P where t
unifies with the left-hand side v by a mgu μ, one of the terms sμ or vμ must not be in normal form.