
Van
Gelder
Freedom
from
Recursive
Negation
The concept of freedom from recursive negation, defined below, is an impor-
tant one for logic programs, and leads to our first main result. The same con-
cept was developed independently in Apt, Blair, and Walker [1988] and
Naqvi [1986], where it was called "stratified" and "layered," respectively.
Other researchers adopted the term "stratified" (Lifschitz [1988],
Przymusinski [1988]) but we prefer our own more descriptive terminology. In
this section we show that programs that are free from recursive negation and
have the bounded term size property are "categorical" under the tight tree
semantics,