下面是该规则集所形成的（部分）推理网络： 2.源程序 /米 An Animal Classifying Expert System */ database xpositive(symbol,symbol) xnegative(symbol,symbol) predicates run animal is(symbol) it is(symbol) positive(symbol,symbol) negative(symbol,symbol) clear_facts remember(symbol,symbol,symbol) ask(symbol,symbol) goal run. clauses run:- animal_is(X),!, write("\nYour animal may be a(n)",X), nl,nl,clear facts. run:- write("\nUnable to determine what"), write("your animal is.\n\n),clear_facts positive(X,Y):-xpositive(X,Y),! positive(X,Y):-not(xnegative(X,Y)),ask(X,Y). negative(X,Y):-xnegative(X,Y),! negative(X,Y):-not (xpositive(X,Y)),ask (X,Y). ask(X,Y): write(X,it "Y,"In"), readln(Reply), remember(X,Y,Reply). remember(X,Y,y):-asserta(xpositive(X,Y)). remember(X,Y,n):-asserta(xnegative(X,Y)),fail. clear_facts:-retract(xpositive(,)),fail. clear_facts:-retract(xnegative(,))fail. clear facts:-write(\n'\nPlease press the space bar to Exit), readchar(). /米 Knowledge Base 米/ animal is(cheetah):- it is(carnivore), positive(has,tawny_color), positive (has,black_spots). animal_is(tiger):- it_is(carnivore), positive(has,tawny_color), positive (has,black stripes). animalis(giraffe):- it_is(ungulate), positive (has,long_neck), positive(has,long_legs), positive(has,dark_spots). animal is(zebra): it_is(ungulate), positive (has,black_stripes). animal is(ostrich):- it_is(bird), negative(does,fly),下面是该规则集所形成的（部分）推理网络： 2. 源程序 /*     An Animal Classifying Expert System      */     database         xpositive(symbol，symbol)         xnegative(symbol，symbol)     predicates         run         animal_is(symbol)         it_is(symbol)         positive(symbol, symbol)         negative(symbol, symbol)         clear_facts         remember(symbol, symbol, symbol)         ask(symbol, symbol) goal         run.     clauses         run:-            animal_is(X),!,            write("\nYour animal may be a(n) ", X),            nl, nl, clear_facts.         run:-            write("\nUnable to determine what"),            write("your animal is. \n\n"), clear_facts.         positive(X, Y):-xpositive(X, Y),!.         positive(X, Y):-not(xnegative(X, Y)), ask(X, Y).         negative(X, Y):-xnegative(X，Y), !.         negative(X, Y):-not(xpositive(X, Y)), ask(X, Y).         ask(X, Y):-            write(X, " it ", Y, "\n"),            readln(Reply),            remember(X, Y, Reply).         remember(X, Y, y):-asserta(xpositive(X, Y)).         remember(X, Y, n):-asserta(xnegative(X, Y)), fail.         clear_facts:-retract(xpositive(_, _)), fail.         clear_facts:-retract(xnegative(_, _)), fail.         clear_facts:-write("\n\nPlease press the space bar to Exit"),                      readchar(_). /*               Knowledge Base           */      animal_is(cheetah):-          it_is(carnivore)，          positive(has, tawny_color),          positive(has, black_spots).      animal_is(tiger):-          it_is(carnivore),          positive(has, tawny_color), positive(has, black_stripes).      animal_is(giraffe):-          it_is(ungulate),          positive(has, long_neck),          positive(has, long_legs),          positive(has, dark_spots). animal_is(zebra):-          it_is(ungulate),          positive(has, black_stripes).      animal_is(ostrich):-          it_is(bird),          negative(does, fly)