2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/161442We give some new characterizations of unitaries, isometries, unital operator spaces, unital function spaces, operator systems, C*-algebras, and related objects. These characterizations only employ the vector space and operator space structure.13 pages. A new last section has been added, on function spacesOperator AlgebrasMathematical PhysicsFunctional Analysistext