An Elementary Proof of the Free-additivity of Voiculescu's Free Entropy
  D. Voiculescu [2] proved that a standard family of independent random unitary k by k matrices and a constant k by k unitary matrix is asymtotically free as k goes to infinity. This result was a key ingredient in Voiculescu's proof [3] that his free entropy is additive when the variables are free. In this paper, we give a very elementary proof of a more detailed version of this result [2]. 
Don Hadwin, Weihua Li, Junhao Shen