Choices without Backtracking

ly, one possiblc3 mode of interaction bctwccn the the problLm solver and the dntn base is as follows. A list is maintained of c~cry ;\ssumptioll set disco\rcrcd to bc contradictory. Whcncvcr the problem solver discovers Iwo val~~cs with contt.adictr~ry assumptions, the combined assumption set is placed on this list, and cvcry vaIlIC b,iscd on it or any of its super sets is crascd from the daL\ base. S~upposc cvcry problem-solving step can bc f<)rmt~liltctl Z: from u clad b dctcminc f(n, b) whcrc f takes some problctn solving work. ‘I’hcn the interaction with the data base of values should bc: li)r all \,,~lircs of form cy : and p : add VUIllC unless the assumption set A,, IJ At, a supcrsct of COIIIC known con\radictory set of assumptions. NOK that this schcrr~c dots not have or r-cquirc any notion of context. ‘I&C; cqui~alcnt noLion in the ~~ssumption-based schcn~~ is just a set of :ls5uniptions: implicitly, it SCt Of ilSSlllllptiOl~S SClCCtS illI tllOSC VillUCS uhosc assumplioll set is a SubSCt Of tllC COntCxt’S ilSSul~lptiOn SCt. It is not ncccss;\ry to bc this cxtrcmc. A more sophisticntcd mode of ilitcr‘lction wo\~ld IX to cxplorc only ;I pilIT Of tllC solution SpXC, ix.. only pcrforni infcrcnccs using th0SC ViIlllC$ WllOSC ilSSLllnptil~llS arc iI subset of the current set of intcrcsting nssuniplions. 'I'llCll. WllCll :I contradiction is discovcrcd, the set of intcrcsting assumptions is chnngcd bul nothing is done to the data base. ‘I’hcsc arc just two of many possible modes of intcmction bctwccn the problem solver and the data base. IiCgilrdlCSS of tllC mode 01 inlcractic;n, the basic assumption-based solution addrcsscs the pi OhlClll:~ discuss4 carlicr: The sittglr skr~c problm. ‘I’hc assumptiotl-t~~lscd schcmc allows arbitrariiy many contradictory solutions to coexist. ‘I’hus, it is simple to compare two solutions. Overzealous cotllrarlicliott avoidmcc. ‘I’hc prcscncc of two contr;~tlic~~>ry assertions dncs not tcrminatc work on the ovcmll knowlcdgc stiltc, rather oniy those assertions arc rcmovcd which dcpcnd on the two contr,ldictory assertions. This is exactly the result dcsircd from a contradiction no more, no ICSS. Snilching slilles is cijicull. Changing state is now trivial or irrclcvant. A state is complctcly spccificd by a set of assumptions.