% P11 (*):  Modified run-length encoding

% encode_modified(L1,L2) :- the list L2 is obtained from the list L1 by 
%    run-length encoding. Consecutive duplicates of elements are encoded 
%    as terms [N,E], where N is the number of duplicates of the element E.
%    However, if N equals 1 then the element is simply copied into the 
%    output list.
%    (list,list) (+,?)

:- ensure_loaded(p10).

encode_modified(L1,L2) :- encode(L1,L), strip(L,L2).

strip([],[]).
strip([[1,X]|Ys],[X|Zs]) :- strip(Ys,Zs).
strip([[N,X]|Ys],[[N,X]|Zs]) :- N > 1, strip(Ys,Zs).