Summary: A Logical Semantics for
DepthFirst Prolog with Ground Negation
Dept. of Computing Science
Simon Fraser University
Burnaby, BC, CANADA V5A 1S6
Abstract: A sound and complete semantics is given for sequential, depthfirst logic
programming with a version of negation as failure. The semantics is logical in the sense
that it is built up only from valuation functions (multivalued logic interpretations in the
style of Fitting and Kunen) and logicallymotivated equivalence relations between formulas.
The notion of predicate folding and unfolding with respect to a program (Tamaki, Sato,
Levi et al.) and the universal notion of ``disjunctive unfolding'' (Andrews) are important
elements of this semantics.
The negation used is the version which returns an error indication whenever it is invoked
on a nonground goal. It is theoretically interesting that this form of negation, along with
the lefttoright processing of depthfirst logic programming, can be characterized logically