On the sum of accretive operators / Paulus Joannes Pius EgbertsRiccati equations in Hilbert spaces : a Popov function approach / Martin WeissConformal quantum field theory in D-dimensions / Efim S. Fradkin and Mark Ya. Palchik ; [transl. from Russian by L. Fradkina]Block lower triangular operators and optimal contractive systems / Derk Roelof PikContributions to the extension theory in Hilbert spaces / Valerică Adrian SandoviciIntroduction to spectral theory in Hilbert space / by Gilbert HelmbergGroup representations on Hilbert subspaces of distributions / Wiebe Roelf Pestman