Bounded continuous witness with neither extremum attained

ID: bounded-continuous-witness-with-neither-extremum-attained

Suppose a topological space admits an unbounded continuous function to . Set and choose so that increases to infinity. There is a continuous function with : interpolate linearly between successive prescribed values and extend constantly below . Then
is continuous and takes values strictly between and , while its values on the even and odd chosen sequences tend to and . Thus neither bound is attained. In particular, unbounded continuous witnesses to noncompactness of a real subspace give this stronger failure of the extreme value theorem for every noncompact real subspace.

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