CREATE TABLE table_11855 ("Client" TEXT, "Windows" TEXT, "GNU/Linux" TEXT, "Mac OS X" TEXT, "Haiku" TEXT)

Which Mac OSX had no haiku and a client that was dc++?
SELECT "Mac OS X" FROM table_11855 WHERE "Haiku" = 'no' AND "Client" = 'dc++'
SELECT "Mac OS X" FROM "table_11855" WHERE "Client" = 'dc++' AND "Haiku" = 'no'