Mos Def brags that he makes the ''treacherous look effortless'' on ''Know That,'' and his solo debut is a tightrope walk across diverse hip-hop styles. He even throws in hardcore punk and a verse of the Red Hot Chili Peppers' ''Under The Bridge.'' Merging old-school bravado with new-school poetics, the Brooklyn legend spouts incisive Afrocentric reality that takes all sides into account. A-

