code: @Override
  	public String debugInfo() {
  		StringBuilder s = new StringBuilder();
  		
  		s.append("possible transactions: ");
  		s.append(allTransactions);
  		s.append('\n');
  		s.append("possible items: ");
  		s.append(allItems);
  		s.append('\n');
  
  		s.append("pairs:\n");
  		s.append(matrix.toString());
  		s.append("info: " + matrix.debugInfo());
  		
  		return s.toString();
  	}
docs: {@inheritDoc}