00303nam a2200121Ia 4500082001800000245004700018260001900065490004700084500000500131700000500136100003400141300000600175  a515.72bAp652  aApproximation of Hilbert space operatorsb  aBostonbPitman  aResearch notes in Mathematicsv v. 72, 102  a  a  aApostal, Costantin and others  a