Help Real Analysis: Proving S(f,x+y) <= S(f,x) + S(f,y)

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SUMMARY

The discussion centers on proving the inequality S(f,x+y) ≤ S(f,x) + S(f,y) for a bounded function f: [0,1] → R, where S(f,x) is defined as the supremum of |f(r) - f(s)| for r, s in [0,1] with |r-s| ≤ x. The suggested approach involves selecting specific values r0 and s0 that satisfy the given condition and demonstrating that g(r0,s0) is less than or equal to M. This method is proposed as a viable starting point for the proof.

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Carl140
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Homework Statement




Let f: [0,1] -> R be a bounded function.

Define S(f,x) = sup { |f(r) - f(s) | : r,s in [0,1] and |r-s| <= x}.

Prove that if x>0, y>0 then:

S(f,x+y) <= S(f,x) + S(f,y).


The Attempt at a Solution



I have no idea how to proceed, could you please help?
 
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The statement to be proved has the form

sup{g(r,s) : r,s \in A and "condition"} <= M.

For the proof, try this: Let r0 and s0 be in A such that "condition." We must show g(r0,s0) <= M.

This method may not work in general, but for this problem I think it does. That will get you started. Write up something and ask again.
 

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