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diligence
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Homework Statement
Suppose F is mapping of a nonempty complete metric space into itself, and that
F^3 = F o F o F is a contraction (o's denote composition). Show that f has a unique fixed point.
The Attempt at a Solution
Isn't this kind of a trick question? Suppose f does not have a unique fixed point. Then there does not exist a unique x such that f(x)=x. Hence there doesn't exist a unique x s.t. f(f(x))=f(x)=x. Hence there doesn't exist a unique x s.t. f(f(f(x)))=f(f(x))=f(x)=x.
But this contradicts the assumption that F^3 is a contraction, since any contraction on a complete metric space has a unique fixed point.
What am I missing here, this is too easy!