Well-Terminating, Input-Driven Logic Programs

We identify a class of predicates for which termination does not depend on left-to-right execution. All that is required is that derivations are input-driven that is, in each derivation step, the input arguments of the selected atom do not become instantiated. The method of showing that a predicate is in that class is based on level mappings, closely following the traditional approach for LD derivations. Many predicates terminate under such weak assumptions. Knowing these predicates can be a very useful part of a more comprehensive method of showing termination, which would have to make more specific assumptions about the selection rule.