Normed linear spaces and Banach spaces; Banach lattices, Abstract approximation theory (approximation in normed linear spaces and other abstract spaces), Approximation by arbitrary linear expressions, Convergence and absolute convergence of Fourier and trigonometric series, Gel'fand diameter, Multipliers in one variable harmonic analysis, space of trigonometric polynomials on the torus, Spaces of measurable functions (\(L^p\)-spaces, Orlicz spaces, Köthe function spaces, Lorentz spaces, rearrangement invariant spaces, ideal spaces, etc.)