Add support for - in list_to_polynomial

polimani.pl

@@ -272,7 +272,6 @@ join_similar_parts_of_term([], []).
 %% simplify_polynomial(+P:atom, -P2:atom) is det
 %
 %  Simplifies a polynomial.
-%  TODO: not everything is a +, there are -
 %
 simplify_polynomial(0, 0) :-
     !.
@@ -399,7 +398,6 @@ simplify_polynomial_list(L, L2) :-
 %% polynomial_to_list(+P:polynomial, -L:List)
 %
 %  Converts a polynomial in a list.
-%  TODO: not everything is a +, there are -
 %
 polynomial_to_list(L - T, [T2 | LS]) :-
     term(T),
@@ -435,13 +433,21 @@ polynomial_to_list(T, [T]) :-
 %% list_to_polynomial(+P:polynomial, -L:List)
 %
 %  Converts a list in a polynomial.
-%  TODO: not everything is a +, there are -
 %
 list_to_polynomial([T1|T2], P) :-
     list_to_polynomial(T2, L1),
     (
         not(L1 = []),
-        P = L1+T1
+        (
+            term_string(T1, S1),
+            string_chars(S1, [First|_]),
+            First = -,
+            term_string(L1, S2),
+            string_concat(S2,S1,S3),
+            term_string(P, S3)
+        ;
+            P = L1+T1
+        )
     ;
         P = T1
     ),