H.G.Muller wrote on Fri, Apr 25, 2008 08:14 PM UTC:
It is not obvious to me that this is two. With two Bishops on each color,
each Bishop now has two othe Bishops with which it can cooperate.
When I have time I will run all combinations BNNN, BBNN, BNBN, BBBN and
BBBB against the 4 Knights, to see how the advantage grows. BBNN is known
to be more than double the BNNN advantage (the difference being the pair
bonus, of about 50cP), while BNBN (like colored Bishops) does give double
the BNNN advantage. But I haven't tried BBBN yet. And this measures very
small differences, so it should use many games (1000+).