set(binary_resolution).
clear(print_initial_clauses).
clear(print_kept).
clear(print_given).
assign(max_seconds,1).
assign(stats,none).

formulas(sos).
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.

formulas(goals).
ancestor(Liz, Billy).
end_of_list.