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).
-S11.   -B11.
-S21.   B21.
S12.    -B12.
S11 | -W11.     S11 | -W12.     S11 | -W21.
S21 | -W11.     S21 | -W21.     S21 | -W22.     S21 | -W31.
S12 | -W11.     S12 | -W12.     S12 | -W22.     S12 | -W13.
-S12 | W11 | W12 | W22 | W13. 
end_of_list.

list(sos).
-W13.
% -W13 | $answer.
end_of_list.