Dual and triple Fourier-Bessel series equations
Integral equations are functional equations, and their history is closely connected with mathematical physics. Malits bases his theory on the Fredholm integral equations. The Swedish mathematician Erik Ivar Fredholm (1866--1927) influenced David Hilbert. Gösta Mittag-Leffler wanted that Fredholm should get the Nobel prize in physics, but it went to Niels Bohr.
scientific article; zbMATH DE number 2153495