:- dynamic(greater/2).

make_rules([]).

make_rules([X]).

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

all_rules([]).

all_rules(Partial_order) :-
  select(X, Partial_order, Partial_order2),
  make_rules(X),
  all_rules(Partial_order2).

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

remove_duplicates([], Unsorted_flat_concise, Unsorted_flat_concise).

remove_duplicates(Unsorted_flat, Unsorted_flat2, Unsorted_flat_concise) :-
  select(X, Unsorted_flat, Unsorted_flat_rest),
  (member(X, Unsorted_flat2),
  remove_duplicates(Unsorted_flat_rest, Unsorted_flat2, Unsorted_flat_concise);
  append([X], Unsorted_flat2, Unsorted_flat3),
  remove_duplicates(Unsorted_flat_rest, Unsorted_flat3, Unsorted_flat_concise)).

my_topo_sort([], Sorted2, Sorted2).

my_topo_sort(Unsorted, Sorted, Sorted2) :-
  get_max(Unsorted, Max, LessList),
  append(Sorted, [Max], NewSorted),
  my_topo_sort(LessList, NewSorted, Sorted2).

my_topo_sort(Unsorted, Sorted) :-
  all_rules(Unsorted),
  flatten(Unsorted, Unsorted_flat),
  remove_duplicates(Unsorted_flat, [], Unsorted_flat_concise),
  my_topo_sort(Unsorted_flat_concise, [], ReverseSorted),
  reverse(ReverseSorted, Sorted),
  write(Sorted).

get_max([], Max, LessList, Max, LessList).

get_max(Unsorted, X, Unsorted2, Max, LessList) :-
  select(Y, Unsorted, Rest),
  (is_greater(X, Y),
  append(Unsorted2, [Y], NewList),
  get_max(Rest, X, NewList, Max, LessList);
  append(Unsorted2, [X], NewList),
  get_max(Rest, Y, NewList, Max, LessList)).

get_max(Unsorted, Max, LessList) :-
  select(X, Unsorted, Unsorted2),
  get_max(Unsorted2, X, [], Max, LessList).