:- dynamic(greater/2).

make_rules([]).

make_rules([X]).

make_rules([X,Y|XS]) :-
  assertz(greater(Y, X)),
  append([Y], XS, XS2),
  make_rules(XS2).

my_topo_sort([], Total_order).

my_topo_sort(Partial_order, Total_order) :-
  select(X, Partial_order, Partial_order2),
  make_rules(X),
  my_topo_sort(Partial_order2, Total_order).

is_greater(Y, X) :-
  greater(Y, X);
  greater(Z, X),
  is_greater(Y, Z).