On exposed positive maps: Robertson and Breuer-Hall maps
  It is well known that so called Breuer-Hall positive maps used in entanglement theory are optimal. We show that these maps possess much more subtle property --- they are exposed. As a byproduct it proves that a Robertson map in the algebra of 4 x 4 complex matrices is not only extreme, which was already shown by Robertson, but also exposed. 
Dariusz Chru\'sci\'nski
quant-ph math-ph math.MP