Note that in some cases several implications are
embedded in a single precept. This is an artifact of
encoding that allows PDL2 to focus on the target (e.g.,
birds flying ability), and deal with the problem in its
limited one-step inference context. However, it also
tends to change the meaning of the corresponding
English statements. For example, the statement
"Animal birds typically fly," in PDL2's resulting
representation, is different from the two statements
"Birds are animals" and "Birds typically fly," in
English. Extensions to the model, that support
forward chaining and a more accurate representation,
are under study.