diff -r 4d030da07c88 -r 3ab0c2e1a4e2 src/chess/rules.h
--- a/src/chess/rules.h	Tue Apr 01 10:28:08 2014 +0200
+++ b/src/chess/rules.h	Tue Apr 01 12:30:25 2014 +0200
@@ -95,6 +95,8 @@
     MoveList* lastmove;
 } GameState;
 
+#define opponent_color(color) ((color)==WHITE?BLACK:WHITE)
+
 #define POS_UNSPECIFIED UINT8_MAX
 #define mdst(b,m) b[(m)->torow][(m)->tofile]
 #define msrc(b,m) b[(m)->fromrow][(m)->fromfile]
@@ -140,6 +142,18 @@
 char getpiecechr(uint8_t piece);
 
 /**
+ * Checks, if a specified field is covered by a piece of a certain color.
+ * 
+ * @param gamestate the current game state
+ * @param row row of the field to check
+ * @param file file of the field to check
+ * @param color the color of the piece that should cover the field
+ * @return TRUE, if any piece of the specified color threatens the specified
+ * field (i.e. could capture an opponent piece)
+ */
+_Bool is_covered(GameState *gamestate,uint8_t row,uint8_t file,uint8_t color);
+
+/**
  * Evaluates a move syntactically and stores the move data in the specified
  * object.
  *