On Nyman, Beurling and Baez-Duarte's Hilbert space reformulation of the   Riemann hypothesis
  There has been a surge of interest of late in an old result of Nyman and Beurling giving a Hilbert space formulation of the Riemann hypothesis. Many authors have contributed to this circle of ideas, culminating in a beautiful refinement due to Baez-Duarte. The purpose of this little survey is to dis-entangle the resulting web of complications, and reveal the essential simplicity of the main results. 
Bhaskar Bagchi