Предикат, проверяющий введена ли цифра, а не буква

domains 
int=integer 
i=int* 
s=string* 
predicates 
arab(int,string) 
numtostr(i,s) 
d(i,string,i) 
wwod(i,i) 
w(i) 
pp(i,i,i) 
clauses 
pp([],Y,Y). 
pp([X1|X],Y,Y2):-Y1=[X1|Y],pp(X,Y1,Y2). 
w([]):-nl. 
w([X|X1]):-write(X," "),w(X1). 
d(X,S,X1):-str_int(S,Z),!,X1=[Z|X]. 
d(X,_,X). 
wwod(X,X2):-write("Vvedite X= "),readln(S),S<>"",!,D(X,S,X1),wwod(X1,X2). 
wwod(X,X1):-pp(X,[],X1). 
arab(0,"Nol"). 
arab(1,"Odin"). 
arab(2,"Dva"). 
arab(3,"Tri"). 
arab(4,"Chetire"). 
arab(5,"Pyat"). 
arab(6,"&#152;Shest"). 
arab(7,"Sem"). 
arab(8,"Vosem"). 
arab(9,"Devyat"). 
numtostr([],[]). 
numtostr([X|Xt],[S|St]):-arab(X,S),numtostr(Xt,St). 
goal 
wwod([],X), 
write("Ishodniy spisok:"), w(X), 
numtostr(X,S), write("Preobrazovanniy spisok:",S).

domains
strl=string*
intl=integer*
 
predicates
num2str(strl,strl)
getDig(integer,strl,string)
 
clauses
 
getDig(0,[H|_],H).
getDig(N,[_|T],R) :- N>0, N1=N-1, getDig(N1,T,R).
 
num2str([],[]).
num2str([X|R],[Q|T]) :- X>="0", X<="9", str_int(X,N), 
                                 getDig(N,["Zero","One","Two","Three","Four",
                                          "Five","Six","Seven","Eight","Nine"],Q), num2str(R,T).
num2str([X|R],[Q|T]) :- X < "0", Q="Not a digit!",num2str(R,T).
num2str([X|R],[Q|T]) :- X > "9", Q="Not a digit!",num2str(R,T).