[Hilbert Space] was established systematically by von Neumann, summarized in his book. The book was based on three papers, published in 1927. Of these three papers, the first introduced the notion of abstract Hilbert space, and presented the "eigenvalue problem", of self-adjoint operators having a continuous part in their spectrum, in a mathematically rigorous form, without making use of Dirac's delta function. The complete, analysis of the spectral theorem was worked out in a following paper in 1930.