Subgoal Protection and Unraveling During Plan Synthesis

s y n t h e s i s when t h e s o l u t i o n o f a l a t e r subgoal. undoes or i n t e r f e r e s w i t h a comp le ted s o l u t i o n to a p r e c e d i n g s u b g o a l . Subgoal a n n i h i l a t i o n d u r i n g p l a n s y n t h e s i s i s d i s c u s s e d , and a u n i f o r m s o l u t i o n t o t h e g e n e r a l p rob lem i s p r e s e n t e d . The two phases o f the t h e o r y a r e d e t e c t i o n and c o r r e c t i o n o f a n n i h i l a t i o n e r r o r s . D e t e c t i o n i s c a r r i e d o u t v i a a t h e o r y o f spontaneous c o m p u t a t i o n i n w h i c h s o c a l l e d g u a r d i a n c l u s t e r s " wa tch over s y n t h e ­ s i z e d g o a l s . C o r r e c t i o n i s accomp l i shed by a g i v e and t ake t e c h n i q u e c a l l e d " u n r a v e l l i n g , " w h e r e i n c o n f l i c t i n g p a r t s o f t he p l a n back o f f t e m p o r a r i l y t o a l l o w o t h e r p a r t s t o c o m p l e t e . The t h e o r e t i c a l f ramework o f the p l a n s y n t h e s i z e r i s d e s c r i b e d , a d e t a i l e d computer example o f d e t e c t i o n and u n r a v e l ­ l i n g i s g i v e n , and o t h e r a p p l i c a t i o n s m o t i v a t e d b y t h i s t h e o r y a re s u g g e s t e d .