Description: Define the adjoint of a Hilbert space operator (if it exists). The
domain of adjh is the set of all adjoint operators. Definition of
adjoint in Kalmbach2 p. 8. Unlike Kalmbach (and most authors), we do
not demand that the operator be linear, but instead show (in adjbdln )
that the adjoint exists for a bounded linear operator. (Contributed by NM, 20-Feb-2006)(New usage is discouraged.)