Unsigned Addition Forms an Abelian Group P68 Closed under addition 0≤ UAdduu,v)≤2w-1 Commutative(交换律) Add(,)=∪Add(v,u) Associative(结合律) UAddw(t, UAddw(u, v)=UAddwqUAddw(t,u,v6 Unsigned Addition Forms an Abelian Group P68 • Closed under addition – 0  UAddw(u , v)  2 w –1 • Commutative （交换律） – UAddw(u , v) = UAddw(v , u) • Associative （结合律） – UAddw (t, UAddw (u,v)) = UAddw (UAddw (t, u ), v)