diff -r 4dcfb4c58b6d -r d726e4b46c33 src/chess/rules.h
--- a/src/chess/rules.h	Thu Apr 17 12:16:14 2014 +0200
+++ b/src/chess/rules.h	Wed May 28 15:47:57 2014 +0200
@@ -38,6 +38,8 @@
 #define INVALID_POSITION    2
 #define AMBIGUOUS_MOVE      3
 #define NEED_PROMOTION      4
+#define PIECE_PINNED        5
+#define KING_IN_CHECK       6
 
 
 #define PIECE_MASK       0x0F
@@ -167,9 +169,10 @@
  * @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 threaten the field
- * @param threats the array where to store the threats (should be able to the
- * rare maximum of 16 elements)
- * @param threatcount a pointer to an uint8_t where to store the amount of threats
+ * @param threats the array where to store the threats (should be able to hold
+ * the rare maximum of 16 elements)
+ * @param threatcount a pointer to an uint8_t where the count of threats is
+ * stored
  * @return TRUE, if any piece of the specified color threatens the specified
  * field (i.e. could capture an opponent piece)
  */
@@ -187,9 +190,10 @@
  * @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 threaten the field
- * @param threats the array where to store the threats (should be able to the
- * rare maximum of 16 elements)
- * @param threatcount a pointer to an uint8_t where to store the amount of threats
+ * @param threats the array where to store the threats (should be able to hold
+ * the rare maximum of 16 elements)
+ * @param threatcount a pointer to an uint8_t where the count of threats is
+ * stored
  * @return TRUE, if any piece of the specified color threatens the specified
  * field (i.e. could capture an opponent piece)
  */
@@ -242,6 +246,22 @@
         uint8_t color);
 
 /**
+ * Checks, if the specified move cannot be performed, because the piece is
+ * either pinned or cannot remove the check.
+ * 
+ * Note: in chess a piece is pinned, when it can't be moved because the move
+ * would result in a check position. But this function <u>also</u> returns true,
+ * if the king is already in check position and the specified move does not
+ * protect the king.
+ * 
+ * @param gamestate the current game state
+ * @param move the move to check
+ * @return TRUE, if the move cannot be performed because the king would be in
+ * check after the move
+ */
+_Bool is_pinned(GameState *gamestate, Move *move);
+
+/**
  * Evaluates a move syntactically and stores the move data in the specified
  * object.
  *