Gleason–Kahane–Żelazko Theorem
Gleason-Kahane-Żelazko Theorem
Theorem that a nonzero linear functional on a unital complex Banach algebra is multiplicative iff it maps each element of the Banach algebra to an element of its spectrum.
Theorem that a nonzero linear functional on a unital complex Banach algebra is multiplicative iff it maps each element of the Banach algebra to an element of its spectrum.
