diff --git a/UBigInt.pas b/UBigInt.pas
index 9fbbf3f..97a81fa 100644
--- a/UBigInt.pas
+++ b/UBigInt.pas
@@ -74,11 +74,12 @@ type
   end;
 
   operator := (const A: Int64): TBigInt;
+  operator - (const A: TBigInt): TBigInt;
   operator + (const A, B: TBigInt): TBigInt;
   operator - (const A, B: TBigInt): TBigInt;
-  operator * (const A: TBigInt; const B: Int64): TBigInt;
+  operator * (const A, B: TBigInt): TBigInt;
   operator shl (const A: TBigInt; const B: Integer): TBigInt;
-  operator = (const A: TBigInt; const B: Int64): Boolean;
+  operator = (const A, B: TBigInt): Boolean;
 
 implementation
 
@@ -418,12 +419,12 @@ begin
     Result := TBigInt.AddAbsoluteValues(A, B, A.IsNegative);
 end;
 
-operator * (const A: TBigInt; const B: Int64): TBigInt;
+operator * (const A, B: TBigInt): TBigInt;
 begin
-  if  (A = 0) or (B = 0) then
+  if  (A = TBigInt.Zero) or (B = TBigInt.Zero) then
     Result := TBigInt.Zero
   else
-    Result := TBigInt.MultiplyAbsoluteValues(A, B, A.IsNegative = (B > 0));
+    Result := TBigInt.MultiplyAbsoluteValues(A, B, A.IsNegative <> B.IsNegative);
 end;
 
 operator shl(const A: TBigInt; const B: Integer): TBigInt;
@@ -475,7 +476,7 @@ begin
   end;
 end;
 
-operator = (const A: TBigInt; const B: Int64): Boolean;
+operator = (const A, B: TBigInt): Boolean;
 begin
   Result := A.CompareTo(B) = 0;
 end;