Prove: Let f be a nondecreasing, but not necessarily continuous, mapping of the closed interval [0,1] into itself. Then f has a
fixed point, i.e., there is some x in [0,1] such that f(x)=x.
(Just to avoid any misunderstanding, [0,1] is the set of all real numbers between 0 and 1, with both 0 and 1 also included.)
(In reply to
Silly corollary by JLo)
Who ? Well, Tarski and Kleene, and all serious computer science students would think this is rather obvious ...