Relationship between LUB and GLB in Bounded Functions

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SUMMARY

The discussion centers on the relationship between the least upper bound (LUB) and greatest lower bound (GLB) in the context of bounded functions defined on Cartesian products. Specifically, it establishes that for a function h: X x Y → R, if the range is bounded, then sup{g(y): y ∈ Y} ≤ inf{f(x): x ∈ X}, where f(x) = sup{h(x,y): y ∈ Y} and g(y) = inf{h(x,y): x ∈ X}. The proof relies on the properties of LUB and GLB, confirming their existence due to the bounded nature of h.

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Homework Statement


h: X x Y --> R is a function from X x Y to R. X,Y nonempty. If range is bounded in R. then let

f : X --> R st f(x) = sup{h(x,y): y belongs to Y} (call this set A)
g :Y --> R st g(y) = inf{h(x,y) : x belongs to X} (call this set B)

Then prove that

sup{g(y) : y belongs to Y} is less than or equal to inf{f(x) : x belongs to X}

Homework Equations



none.

The Attempt at a Solution



As h(X,Y) is bounded the LUB and GLB exist. Now for each x, A is a subset of h(x,y). thus f(x) is <= LUB.
thus inf f(x) <= LUB.

Similarly I got, sup g(y) >= GLB.

But this leaves me nowhere :(
 
Last edited:
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well I've got it, thanks anyways.
 

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