%deln([1, 2, 3, 4, 5, 6, 7], R).
%delindex([1, 1, 1, 2, 2, 2, 2, 3, 4, 5, 5, 6, 7], R).
%start([1,2,3,4,5,6,7,8,9,10], R).
/*
deln([],[]).
deln([Xh|Xt],Y):- 
0 is Xh mod 3, 
deln(Xt,Y).
deln([Xh|Xt],[Xh|Yt]):- 
deln(Xt, Yt).
*/

/*
delindex(_,[],[]).

delindex(N,[Xh|Xt],Y):- 
 0 =:= N mod 3,
 N1 is N + 1,
 delindex(N1,Xt,Y).

delindex(N,[Xh|Xt],[Xh|Yt]):- 
 N1 is N + 1, 
 delindex(N1, Xt, Yt).

start(X, R) :- delindex(1, X, R).

delindex(_,[],[]).*/



%delindex([Xh|Xt],Y):- 
% delindex(Xt,Y).

delindex([], []).
delindex([A], [A]).
delindex([H,A],[H,A]).
delindex([H,A,_|T],[H,A|R]) :- delindex(T, R).