What is the best that you can say about a function with given property
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Let $E subset mathbb R$, and $f:Erightarrow mathbb R$, be a map. Set $$Delta_{varepsilon,a} = {delta>0: B(f(a),delta)supset f(Ecap B(a,varepsilon))} for varepsilon>0,ain E$$
$$A_{n,delta}={ain E:Ecap B(a,delta)⊂ f^{−1}(B(f(a),frac{1}{n}))} for n in mathbb N, delta>0$$
where $B(x,r)$ denotes the interval $(x-r,x+r)$(i.e. ball of radius r in real metric space).Then,
$(i)$If $$bigcup_{varepsilon>0}bigcap_{ain E}Delta_{varepsilon,a} = (0,infty)$$Then what is the best that you can say about f without any extra assumption on the hypothesis?
$(ii)$If $$bigcap_{n in mathbb N}bigcup_{delta>0}A_{n,delta} = E$$
Then what is the best that you can say about f without any extra assumption on the hypothesis?
I am not getting the notation in this question about lots of unions and intersections and also I have a hunch that both of these imply continuity or uniform continuity or something similar.
Please help. Thanks in advance.
general-topology continuity epsilon-delta uniform-continuity
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up vote
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Let $E subset mathbb R$, and $f:Erightarrow mathbb R$, be a map. Set $$Delta_{varepsilon,a} = {delta>0: B(f(a),delta)supset f(Ecap B(a,varepsilon))} for varepsilon>0,ain E$$
$$A_{n,delta}={ain E:Ecap B(a,delta)⊂ f^{−1}(B(f(a),frac{1}{n}))} for n in mathbb N, delta>0$$
where $B(x,r)$ denotes the interval $(x-r,x+r)$(i.e. ball of radius r in real metric space).Then,
$(i)$If $$bigcup_{varepsilon>0}bigcap_{ain E}Delta_{varepsilon,a} = (0,infty)$$Then what is the best that you can say about f without any extra assumption on the hypothesis?
$(ii)$If $$bigcap_{n in mathbb N}bigcup_{delta>0}A_{n,delta} = E$$
Then what is the best that you can say about f without any extra assumption on the hypothesis?
I am not getting the notation in this question about lots of unions and intersections and also I have a hunch that both of these imply continuity or uniform continuity or something similar.
Please help. Thanks in advance.
general-topology continuity epsilon-delta uniform-continuity
add a comment |
up vote
0
down vote
favorite
up vote
0
down vote
favorite
Let $E subset mathbb R$, and $f:Erightarrow mathbb R$, be a map. Set $$Delta_{varepsilon,a} = {delta>0: B(f(a),delta)supset f(Ecap B(a,varepsilon))} for varepsilon>0,ain E$$
$$A_{n,delta}={ain E:Ecap B(a,delta)⊂ f^{−1}(B(f(a),frac{1}{n}))} for n in mathbb N, delta>0$$
where $B(x,r)$ denotes the interval $(x-r,x+r)$(i.e. ball of radius r in real metric space).Then,
$(i)$If $$bigcup_{varepsilon>0}bigcap_{ain E}Delta_{varepsilon,a} = (0,infty)$$Then what is the best that you can say about f without any extra assumption on the hypothesis?
$(ii)$If $$bigcap_{n in mathbb N}bigcup_{delta>0}A_{n,delta} = E$$
Then what is the best that you can say about f without any extra assumption on the hypothesis?
I am not getting the notation in this question about lots of unions and intersections and also I have a hunch that both of these imply continuity or uniform continuity or something similar.
Please help. Thanks in advance.
general-topology continuity epsilon-delta uniform-continuity
Let $E subset mathbb R$, and $f:Erightarrow mathbb R$, be a map. Set $$Delta_{varepsilon,a} = {delta>0: B(f(a),delta)supset f(Ecap B(a,varepsilon))} for varepsilon>0,ain E$$
$$A_{n,delta}={ain E:Ecap B(a,delta)⊂ f^{−1}(B(f(a),frac{1}{n}))} for n in mathbb N, delta>0$$
where $B(x,r)$ denotes the interval $(x-r,x+r)$(i.e. ball of radius r in real metric space).Then,
$(i)$If $$bigcup_{varepsilon>0}bigcap_{ain E}Delta_{varepsilon,a} = (0,infty)$$Then what is the best that you can say about f without any extra assumption on the hypothesis?
$(ii)$If $$bigcap_{n in mathbb N}bigcup_{delta>0}A_{n,delta} = E$$
Then what is the best that you can say about f without any extra assumption on the hypothesis?
I am not getting the notation in this question about lots of unions and intersections and also I have a hunch that both of these imply continuity or uniform continuity or something similar.
Please help. Thanks in advance.
general-topology continuity epsilon-delta uniform-continuity
general-topology continuity epsilon-delta uniform-continuity
asked Nov 15 at 12:34
Crazy for maths
5109
5109
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1 Answer
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Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
ii. says $f$ is continuous on $E$.
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
1
down vote
accepted
Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
ii. says $f$ is continuous on $E$.
add a comment |
up vote
1
down vote
accepted
Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
ii. says $f$ is continuous on $E$.
add a comment |
up vote
1
down vote
accepted
up vote
1
down vote
accepted
Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
ii. says $f$ is continuous on $E$.
Yes, i. says $f$ is uniformly continuous on $E$, (for example, for any $eta>0$, there is $epsilon$ so that $etain cap_a Delta_{epsilon, a}$, this says $|x-a|<epsilon$ implies $|f(x)-f(a)|<eta$...)
ii. says $f$ is continuous on $E$.
answered Nov 15 at 18:27
Yu Ding
1494
1494
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