domains 
    x = char
    l = char*
    
predicates
    palindrome(l)
    reverse(l,l)
    concatenate(l,l,l)
    
clauses
    concatenate([],List,List).
    
    concatenate([X|List1],List2,[X|List3]) :-
        concatenate(List1,List2,List3).
        
    reverse([],[]).
    
    reverse([X|Tail],List) :-
        reverse(Tail,Tail1),
        concatenate(Tail1,[X],List).
        
    palindrome(List) :-
        reverse(List,List).