qChapter 14 treats *H**¥* control with some simplified assumptions: *R**1**=I, R**2**=I, D**12***C**1**=0, *and *B**1**D**21***=0. *We show that there exists an
admissible controller such that *||**T**zw**||**¥** **<**g* if and only if the
following three conditions hold:

(i) *H**¥** **Î**dom(Ric) *and *X**¥** :=Ric(H**¥**)>0, *where

(ii) *J**¥** **Î**dom(Ric) *and *Y**¥** :=Ric(J**¥**)>0, *where

(iii) r(*X**¥**Y**¥**)< **g**2**.*

Chapter
14