clear(print_given).
set(binary_res).
clear(detailed_history).
clear(print_kept).
clear(print_back_sub).
assign(max_seconds,1).
assign(stats_level,0).

list(usable).
mother(Liz,Charley).
father(Charley,Billy).
-mother(x,y) | parent(x,y).
-father(x,y) | parent(x,y).
-parent(x,y) | ancestor(x,y).
-parent(x,y) | -ancestor(y,z) | ancestor(x,z).
end_of_list.

list(sos).
-ancestor(Liz, Billy).
% -ancestor(Liz, Billy) | $answer.
end_of_list.