C* algèbres

Les hermitiens, ce sont visiblement les x de A qui vérifient x* = x , c.-à-d. les auto-adjoints. Pour le reste, lisons wikipedia :

* The set of self-adjoint elements of a C*-algebra A naturally has the structure of a partially ordered vector space; the ordering is usually denoted ≥. In this ordering, a self-adjoint element x of A satisfies x ≥ 0 if and only if the spectrum of x is non-negative. Two self-adjoint elements x and y of A satisfy x ≥ y if x - y ≥ 0.