diff --git a/polymani.pl b/polymani.pl
index 11c5dd6..5854e02 100644
--- a/polymani.pl
+++ b/polymani.pl
@@ -298,10 +298,20 @@ parse_number_explicit(void, void, T, [WN | In], NC) :-
     member(P, [f, g, fy]),
     !,
     parse_number_explicit(P, N, T, In, NC).
+parse_number_explicit(fy, NL, T, [WN | In], NC) :-
+    special_word_number(WN, N, f),
+    !,
+    parse_number_explicit(f, op(-, NL, N), T, In, NC).
 parse_number_explicit(fy, NL, T, [WN | In], NC) :-
     special_word_number(WN, N, f),
     !,
     parse_number_explicit(f, op(+, NL, N), T, In, NC).
+parse_number_explicit(xfy, TL, T, [WN | In], NC) :-
+    TL \= void,
+    special_word_number(WN, N, P),
+    member(P, [f, g, fy]),
+    !,
+    parse_number_explicit(P, op(-, TL, N), T, In, NC).
 parse_number_explicit(xfy, TL, T, [WN | In], NC) :-
     TL \= void,
     special_word_number(WN, N, P),
@@ -400,6 +410,7 @@ parse_power(TB) -->
     parse_polynomial_variable(TB).
 
 
+parse_operation(-) --> [minus].
 parse_operation(+) --> [plus].
 parse_operation(*) --> [times].
 
@@ -473,6 +484,11 @@ parse_polynomial_explicit(void-_, T) -->
     parse_operation(Op),
     !,
     parse_polynomial_explicit(op(Op, TL, TRP)-TRP, T).
+parse_polynomial_explicit(TLP-TL, T) -->
+    parse_polynomial_operand(TL),
+    parse_operation(-),
+    !,
+    parse_polynomial_explicit(op(-, TLP, TRP)-TRP, T).
 parse_polynomial_explicit(TLP-TL, T) -->
     parse_polynomial_operand(TL),
     parse_operation(+),
@@ -539,6 +555,12 @@ parse_command(multiply(TN, TP)) -->
     parse_number(TN),
     [by],
     parse_polynomial(TP).
+parse_command(op(-, TN, TP)) -->
+    [sub],
+    parse_polynomial(TN),
+    [X],
+    { member(X, [to, with]) },
+    parse_polynomial(TP).
 parse_command(op(+, TN, TP)) -->
     [add],
     parse_polynomial(TN),