Byzantine Blackwood
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Developed by J.C.H. Marx from Great Britain. It is a complex system 
used to show the aces, kings and queens of key suits. It is used only
when there are one or two key suits. 

Key suits are:  
* the trump suit
* any geniune suit bid and supported by the partnership
* any suit bid by a player IF their partner's first bid was in NT
  (for example, with 1H-2NT, hearts is a key suit)

If there is only one key suit, the king of a half-key suit may be 
shown. A half-key suit is a geniune suit that is bid but not supported. 

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If there is only one key suit, the responses to 4NT are:
{notation:  A = ace, kK = key suit king, kQ = key suit queen, 
	    hK = half-key suit king } 

5C  0A; 3A; or 2A+kK
5D  1A; 4A; or 3A+kK
5H  2A; A+kK+kQ; or kA+kK+hK  (where kA = key suit Ace)
5S  2A+kK+kQ; or 3A+hK
5NT 3A+kK+kQ; or 4A+kK

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If there two key suits, half-key suits are not shown, and the responses
to 4NT are:
{more notation:  k(A+K+Q) = ace, king and queen of the same key suit} 

5C  0A; 3A; or 2A+kK
5D  1A; 4A; or 3A+kK
5H  2A; k(A+K+Q); or A+2kK 
5S  2A+k(K+Q); 2A+2kK; or A+kK+k(K+Q)
5NT 3A+k(K+Q); 3A+2kK; 4A+kK; 2A+kK+k(K+Q); or A+2k(K+Q)