Крестики нолики для 2 игроков - Prolog

Формулировка задачи:

Помогите переделать код, чтобы было 2 игрока, а не игрок и компьютер. Мною это непостижимо...

database
db(integer,integer,symbol)   
Predicates
predicates 
pole
go(integer,symbol,symbol) 
protect(symbol,symbol) 
type(integer,symbol)    
etc(symbol,symbol) 
goal 
write("who starts?"),nl, write("1 - I, 0 - Computer."), 
readint(Who),write("type?"),nl,write("1 - X, 0 - O."), 
readint(What),type(What,I1),etc(I1,I2),go(Who,I1,I2),!, 
nl,nl; write("Error."),nl. 
clauses 
db(1,1,"-"). db(1,2,"-"). db(1,3,"-"). db(2,1,"-").db(2,2,"-"). 
db(2,3,"-"). db(3,1,"-"). db(3,2,"-"). db(3,3,"-"). 
 
type(1,x). type(0,o). etc(x,o). etc(o,x). 
 
go(0,Comp,_):- protect(Comp,Comp),!,pole,nl,write("You are a loser."). 
go(0,Comp,You):- protect(Comp,You),!,pole,go(1,You,Comp). 
go(0,Comp,You):- retract(db(2,2,"-")),!,assert(db(2,2,Comp)), 
  pole,go(1,You,Comp). 
go(0,Comp,You):- db(R,St,"-"), (R+St) mod 2=0,retract(db(R,St,"-")),!, 
  assert(db(R,St,Comp)),pole,go(1,You,Comp). 
go(0,Comp,You):- retract(db(R,St,"-")),!,assert(db(R,St,Comp)), 
  pole,go(1,You,Comp). 
go(1,You,Comp):- db(_,_,"-"),write("next:","line (ot 1 do 3): "), 
  readint(R),R>0,R<4,write("column (ot 1 do 3): "), 
  readint(St),St>0,St<4,retract(db(R,St,"-")),!, 
  assert(db(R,St,You)),go(0,Comp,You). 
go(_,_,_):- not(db(_,_,"-")),nl,write("Draw."). 
 
protect(Comp,You):- db(N1,St,You),db(N2,St,You),N1<>N2, 
  retract(db(N3,St,"-")),!,assert(db(N3,St,Comp)); 
  db(R,N1,You),db(R,N2,You),N1<>N2,retract(db(R,N3,"-")),!, 
  assert(db(R,N3,Comp)); 
  db(I,I1,You),I=I1,db(J,J1,You),J=J1,I<>J,db(K,K1,"-"),K=K1, 
  retract(db(K,K1,"-")),!,assert(db(K,K1,Comp)); 
  db(I,J,You),I+J=4,db(N,K,You),N<>I,N+K=4,db(M,L,"-"),M+L=4, 
  retract(db(M,L,"-")),!,assert(db(M,L,Comp)). 
 
pole:- db(1,1,S1),db(1,2,S2),db(1,3,S3),db(2,1,S4),db(2,2,S5), 
  db(2,3,S6),db(3,1,S7),db(3,2,S8),db(3,3,S9),!,nl,nl, 
  write(S1,S2,S3),nl,write(S4,S5,S6),nl,write(S7,S8,S9),nl,nl.

Решение задачи: «Крестики нолики для 2 игроков»

textual
                            Листинг программы 
                        

                            database
db(integer,integer,symbol)   
Predicates
predicates
new 
pole
nondeterm go(symbol,symbol) 
goal 
retractall(db(_,_,_)),new,go("X","O"),!,nl. 
 
clauses 
new:-assert(db(1,1,"-")),assert(db(1,2,"-")),assert(db(1,3,"-")),
    assert(db(2,1,"-")),assert(db(2,2,"-")),assert(db(2,3,"-")),
    assert(db(3,1,"-")),assert(db(3,2,"-")),assert(db(3,3,"-")).
 
db(1,1,"-"). db(1,2,"-"). db(1,3,"-"). db(2,1,"-").db(2,2,"-"). 
db(2,3,"-"). db(3,1,"-"). db(3,2,"-"). db(3,3,"-"). 
 
go(_,_):- db(X,1,Gamer),Gamer<>"-",db(X,2,Gamer),db(X,3,Gamer),write(Gamer," win!\n"),!. 
go(_,_):- db(1,X,Gamer),Gamer<>"-",db(2,X,Gamer),db(3,X,Gamer),write(Gamer," win!\n"),!. 
go(_,_):- db(1,1,Gamer),Gamer<>"-",db(2,2,Gamer),db(3,3,Gamer),write(Gamer," win!\n"),!.
go(_,_):- db(1,3,Gamer),Gamer<>"-",db(2,2,Gamer),db(3,1,Gamer),write(Gamer," win!\n"),!.     
go(Gamer1,Gamer2):-write("Gamer ",Gamer1,":\n","line (ot 1 do 3): "), 
  readint(R),R>0,R<4,write("column (ot 1 do 3): "), 
  readint(St),St>0,St<4,db(R,St,"-"),!,retract(db(R,St,"-")),
  assert(db(R,St,Gamer1)),pole,go(Gamer2,Gamer1).
go(Gamer1,Gamer2):-write("Error!\n"),go(Gamer1,Gamer2).
 
pole:- db(1,1,S1),db(1,2,S2),db(1,3,S3),db(2,1,S4),db(2,2,S5), 
  db(2,3,S6),db(3,1,S7),db(3,2,S8),db(3,3,S9),!,nl,nl, 
  write(S1,S2,S3),nl,write(S4,S5,S6),nl,write(S7,S8,S9),nl,nl.
                        