Harmonic analysis on Euclidean spaces Approximation theory 2 Approximations and expansions 2 Functional analysis 2 Functions of a complex variable 2 Functions of complex variables 2 Number theory 2 Operator theory 2 Probability theory and stochastic processes 2 Real functions 2 Fourier transformations 1 Harmonic analysis 1 Instructional exposition (textbooks, tutorial papers, etc.) 1