 One of his most well-known contributions was the invention and study of the Generalised Fock space F, a Reproducing Kernel Hilbert Space of input-output maps of generic nonlinear dynamical systems, and used a "linear" orthogonal projection in F for optimal recovery of such "nonlinear" maps from the input-output data.This approach extended to nonlinear systems the powerful orthogonal projection method, previously used exclusively for linear systems.The analytics behind this approach are represented as neural networks, which ultimately led to the development of Figueiredo’s Optimal Interpolation neural network and CDL neural network.