[rules-users] One question about "NOT"

Hi all, I checked the manual about "not", and it says: ==quote== not' is first order logic's Non-Existential Quantifier and checks for the non existence of something in the Working Memory. Think of 'not' as meaning "there must be none of...". " ==end== So there is no negation-as-failure, no stable model semantics, no well founded semantics in Drools. Is it the case? Thanks, Senlin