isList([]):-write('we got []'),nl.
isList([_|T]):-write(T),nl,isList(T).
/*;;isList([a,b])
//;;isList([a|[b]])
//;;isList([b])
//;;isList([b|[]])
//;;isList([])
*/
isListX([]).
isListX([_|T]):-isListX(T).

isListY([]):-write('we got []'),nl.
isListY([_,_|[A,B|T]]):-write(T),nl,isListY(T).

/*
[i,am,a,computer]
[you,are,a,human]
*/
alter([],[]).
alter([H1|T1],[H2|T2]):-change(H1,H2),alter(T1,T2).

change(i,you).
change(am,are).
change(a,a).
change(computer,human).
change(horse,animal).
change(we,you).

append([],B,B).
append([H|T1],B,[H|T2]):-append(T1,B,T2).

listlen([],0).
listlen([H|T],N):-listlen(T,N1),N is N1 +1.

/*
lenacc([H|T],0,N):-A1 is A +1, lenacc(T,A1,N).
*/
lenacc(L,N):-lenacc(L,0,N).
lenacc([],A,A):-
	write('[]'),write(' '),
	write(A),write(' '),
	nl.
lenacc([H|T],A,N):-
	write(H),write(' '),
	write(T),write(' '),
	write(A),write(' '),
	write(N),write(' '),
	nl,
	A1 is A +1, 
	lenacc(T,A1,N).