Question: Who developed one of the foundations of functional analysis and also taught Hugo Steinhaus?
Sentence (from "Steinhaus–Johnson–Trotter algorithm"): The Steinhaus–Johnson–Trotter algorithm or Johnson–Trotter algorithm, also called plain changes, is an algorithm named after Hugo Steinhaus, Selmer M. Johnson and Hale F. Trotter that generates all of the permutations of "n" elements.
Relevant evidence: No