existence of inverses, adjoint operators, General (adjoints, conjugates, products, inverses, domains, ranges, etc.), Integral, integro-differential, and pseudodifferential operators, reproducing kernels, Inner product spaces and their generalizations, Hilbert spaces, Linear operators on function spaces (general), inverse operator, Tensor products in functional analysis, Hilbert spaces with reproducing kernels, Hilbert spaces of continuous, differentiable or analytic functions, conjugate operator