== | B  C  D  F  I  S 
---+------------------
 B | B  *  *  *  *  * 
 C | *  B  *  *  *  * 
 D | *  *  B  *  *  * 
 F | *  *  *  B  *  * 
 I | *  *  *  *  B  * 
 S | *  *  *  *  *  B