Prominent American Mathematician of the 20th century. In 1939, Sheffer published the influential work "Some Properties of Polynomial Sets of Type Zero." The "Sheffer Sequence" is named for him. Autograph letter signed "Isador Mitchell Sheffer". 1 page. 8-1/2"x11". July 1, 1948. No place. To Dr. WIlliam N. Huff, fellow mathematician.....