Characterization of equality in a generalized Dunkl--Williams inequality
  We establish a generalization of the Dunkl--Williams inequality and its inverse in the framework of Hilbert $C^*$-modules and characterize the equality case. As applications, we get some new results and some known results due to Pe\v{c}ari\'c and Raji\'c [Linear Algebra Appl. 425 (2007), no. 1, 16--25]. 
Mohammad Sal Moslehian and Farzad Dadipour
math.FA math.OA