////
inline Color operator+ (Color c, int i) { return Color(int(c) + i); }
-inline void operator++ (Color &c, int i) { c = Color(int(c) + 1); }
+inline void operator++ (Color &c, int) { c = Color(int(c) + 1); }
inline Color opposite_color(Color c) {
return Color(int(c) ^ 1);