证::x(m)为因果序列 ZD∑x(m=∑D∑x(m)"=∑x(m)∑ n=0m=0 n=m m m=n ∑ x(m 11→|>1 x(m)2 n ∑ X(=)|>R zl> max R证: x(n)为因果序列 0 0 0 [ ( )] [ ( )] n n n m n m ZT x m x m z 0 ( ) n m n m x m z 1 1 0 ( ) 1 1 1 m m z x m z z z 1 0 1 ( ) 1 m m x m z z ( ) 1 x z X z z R z max ,1 x z R n m m=n 0