Default Logic

Last updated Nov 8, 2022 Edit Source

A closed default is one that has been instantiated The In-set contains all the consequences from applying a default The Out-set contains all the negations of the justifications from applying a default: these are the predicates which cannot be proven true by the In-Set for the extension to be consistent

1. Start with the root node: Out is initialized to $\emptyset$ while In is set to the current knowledge base
2. For every node, check for direct applicability of defaults (If no defaults are directly applicable: we arrived at a closed process) direct applicability must satisfy 2 conditions:
   1. Default must be triggered: In-set contains the prerequisite
   2. Default must be justified: negation of justifications cannot be proven True from the current In-set
3. If the new In-set becomes inconsistent ($In \cap Out \neq \emptyset$ or $In\cup \delta .consq \\ \vdash Out$) : process is unsuccessful

We arrive at an extension for every closed and successful process.