Who developed one of the foundations of functional analysis and also taught Hugo Steinhaus?
Hugo Steinhaus: Władysław Hugo Dionizy Steinhaus (January 14, 1887 – February 25, 1972) was a Polish mathematician and educator. Hugo Steinhaus:  Steinhaus obtained his PhD under David Hilbert at Göttingen University in 1911 and later became a professor at the Jan Kazimierz University in Lwów (now Lviv, Ukraine), where he helped establish what later became known as the Lwów School of Mathematics. David Hilbert: David Hilbert (] ; 23 January 1862 – 14 February 1943) was a German mathematician. David Hilbert:  He also formulated the theory of Hilbert spaces, one of the foundations of functional analysis.
David Hilbert