TY - JOUR AU - Peralta Pereira, Antonio Miguel PY - 2018 UR - http://hdl.handle.net/10481/58094 AB - Let E and P be subsets of a Banach space X, and let us define the unit sphere around E in P as the set Sph(E; P) := {x is an element of P : parallel to x - b parallel to = 1 for all b is an element of E}. Given a C-algebra A and a subset E... LA - eng PB - Springer Nature TI - Characterizing projections among positive operators in the unit sphere DO - 10.15352/aot.1804-1343 ER -