Partial *-algebras of closed operators and their commutants. I. General structure
Partial *-algebras of closed operators and their commutants. II. Commutants and bicommutants
Partial Hilbert spaces and amplitude functions
Positive linear maps of matrix algebras
A characterization of the structure of positive maps is presented. This sheds some more light on the old open problem studied both in Quantum Information and Operator Algebras. Our arguments are based on the concept of exposed points, links between tensor products and mapping spaces and convex analysis.