Let △ be the unit disk,and H1(△) be the follwing set
H1 (△)={φ(z):φ(z) is analytic in △,|φ(z)|<1,
and there exists a θ∈[0,2π]such that|φ(eiθ<)|=1} Then all the proper contraction on H,we have
φ∈H1sup(△) b2(φ)=2,φ∈H1sup(△)b2(φ)=1 where b2(φ)=supA(||φ'(A)||(1-||A||2)+||φ(A)||2)
b2(φ)=supA(||φ'(A)||(1-||A||2)+infx∈H||x||=1||φ(A)x||2)On the other hand,if φ(z)=Σk=0n akzk,|φ(z)|<1, then
||φ'(A)||+||φ'(A)|| ≤ 2n where φ(z)=znφ(z-1), and 2 is the best constant for all the choices of n,φ(z) and A.