“…If the forward operator F and hence the operator equation (1) is linear, then in Hilbert spaces a comprehensive and rather complete regularization theory, including a general regularization schema and a well-established collection of methods, assertions on stability, convergence, and convergence rates, is available since more than 20 years; see [10,35,[77][78][79]84]. For recent progress of regularization theory applied to linear ill-posed problems, please refer to the papers [16,22,31,57,61,80,85,86,90].…”