a1 University of Iowa, Iowa City, Iowa 52240, U.S.A.
Let X be a Banach space and K a convex subset of X. A mapping Tof K into K is called a nonexpansive mapping if | T(x) – T(y) | ≦ | x – y | for all x, yεK.
(Received September 16 1969)
(Revised December 26 1969)
† Research supported by the National Science Foundation, grant GP8367.