Marcos A. Kiwi Carsten Lund Daniel A. Spielman Alexander Russell Ravi Sundaram Alternation in interaction. 202-246 2000 9 Computational Complexity 3-4 http://link.springer.de/link/service/journals/00037/bibs/0009003/00090202.htm db/journals/cc/cc9.html#KiwiLSRS00