2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/154469A calculus of sequences started in 1936 opened the way for future extensions of umbral calculus in its finite operator form. Because of historically established notation we call it the psi-calculus.It appears in parts to be almost automatic extension of the standard classical finite operator calculus.CombinatoricsDiscrete Mathematics05A40, 81S99text