A parametric version of the Borsuk Ulam theorem
Clash Royale CLAN TAG#URR8PPP
$begingroup$
Is there a topological space $X$, which is not a singleton, and satisfies the following property?
For every continuous function $f: Xtimes S^2tomathbbR^2$ there exist a point $xin S^2$ such that $f(t, x)=f(t,-x),;forall t in X$?
Is there a classification of all spaces $X$ with such property?
at.algebraic-topology gn.general-topology
$endgroup$
add a comment |
$begingroup$
Is there a topological space $X$, which is not a singleton, and satisfies the following property?
For every continuous function $f: Xtimes S^2tomathbbR^2$ there exist a point $xin S^2$ such that $f(t, x)=f(t,-x),;forall t in X$?
Is there a classification of all spaces $X$ with such property?
at.algebraic-topology gn.general-topology
$endgroup$
3
$begingroup$
Who downvoted this? It's a totally reasonable question!
$endgroup$
– Dylan Wilson
Jan 4 at 18:08
$begingroup$
At least we may consider any set $X$ with the trivial topology:)
$endgroup$
– Aleksei Kulikov
Jan 4 at 18:17
3
$begingroup$
A less stringent condition would be that there is a continuous (instead of constant) map $tto x(t)$ with $f(t,x(t))=f(t,-x(t))$.
$endgroup$
– BS.
Jan 5 at 11:07
add a comment |
$begingroup$
Is there a topological space $X$, which is not a singleton, and satisfies the following property?
For every continuous function $f: Xtimes S^2tomathbbR^2$ there exist a point $xin S^2$ such that $f(t, x)=f(t,-x),;forall t in X$?
Is there a classification of all spaces $X$ with such property?
at.algebraic-topology gn.general-topology
$endgroup$
Is there a topological space $X$, which is not a singleton, and satisfies the following property?
For every continuous function $f: Xtimes S^2tomathbbR^2$ there exist a point $xin S^2$ such that $f(t, x)=f(t,-x),;forall t in X$?
Is there a classification of all spaces $X$ with such property?
at.algebraic-topology gn.general-topology
at.algebraic-topology gn.general-topology
edited Jan 4 at 17:48
Ali Taghavi
asked Jan 4 at 17:40
Ali TaghaviAli Taghavi
12352083
12352083
3
$begingroup$
Who downvoted this? It's a totally reasonable question!
$endgroup$
– Dylan Wilson
Jan 4 at 18:08
$begingroup$
At least we may consider any set $X$ with the trivial topology:)
$endgroup$
– Aleksei Kulikov
Jan 4 at 18:17
3
$begingroup$
A less stringent condition would be that there is a continuous (instead of constant) map $tto x(t)$ with $f(t,x(t))=f(t,-x(t))$.
$endgroup$
– BS.
Jan 5 at 11:07
add a comment |
3
$begingroup$
Who downvoted this? It's a totally reasonable question!
$endgroup$
– Dylan Wilson
Jan 4 at 18:08
$begingroup$
At least we may consider any set $X$ with the trivial topology:)
$endgroup$
– Aleksei Kulikov
Jan 4 at 18:17
3
$begingroup$
A less stringent condition would be that there is a continuous (instead of constant) map $tto x(t)$ with $f(t,x(t))=f(t,-x(t))$.
$endgroup$
– BS.
Jan 5 at 11:07
3
3
$begingroup$
Who downvoted this? It's a totally reasonable question!
$endgroup$
– Dylan Wilson
Jan 4 at 18:08
$begingroup$
Who downvoted this? It's a totally reasonable question!
$endgroup$
– Dylan Wilson
Jan 4 at 18:08
$begingroup$
At least we may consider any set $X$ with the trivial topology:)
$endgroup$
– Aleksei Kulikov
Jan 4 at 18:17
$begingroup$
At least we may consider any set $X$ with the trivial topology:)
$endgroup$
– Aleksei Kulikov
Jan 4 at 18:17
3
3
$begingroup$
A less stringent condition would be that there is a continuous (instead of constant) map $tto x(t)$ with $f(t,x(t))=f(t,-x(t))$.
$endgroup$
– BS.
Jan 5 at 11:07
$begingroup$
A less stringent condition would be that there is a continuous (instead of constant) map $tto x(t)$ with $f(t,x(t))=f(t,-x(t))$.
$endgroup$
– BS.
Jan 5 at 11:07
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
Theorem. For a topological space $X$ the following conditions are equivalent:
1) for any continuous map $f:Xtimes S^2tomathbb R^2$ there exists a point $sin S^2$ such that $f(x,s)=f(x,-s)$ for any $xin X$;
2) any continuous map $f:Xto mathbb R$ is constant.
Proof. (1) $Rightarrow$ (2) Assume that $X$ admits a non-constant map $hbar :Xto mathbb R$. We lose no generality assuming that $0,1subset hbar(X)subset[0,1]$.
Then there are points $x_0,x_1in X$ such that $hbar(x_i)=i$ for $iin0,1$.
Let $p:S^2tomathbb R^2$, $p:(x,y,z)mapsto (x,y)$, be the projection of the sphere $S^2=(x,y,z)inmathbb R^3:x^2+y^2+z^2=1$ onto the plane.
Let $varphi:S^2to S^2$ be any homeomorphism of the sphere $S^2$ such that $pcirc varphi(0,0,1)ne pcirc varphi(0,0,-1)$.
Using the Tietze-Urysohn Theorem, find a continuous map $psi:[0,1]times S^2tomathbb R^2$ such that $psi(0,s)=p(s)$ and $psi(1,x)=pcircvarphi(s)$ for all $sin S$. Then the continuous map $$f:Xtimes S^2tomathbb R^2,;;f:(x,s)mapsto psi(hbar(x),s),$$ has the following property:
if $f(x_0,s)=f(x_0,-s)$ for some $sin S^2$, then $sin(0,0,1),(0,0,-1)$ and $f(x_1,s)ne f(x_1,-s)$.
(2) $Rightarrow$ (1) Assume that each continuous map $Xtomathbb R$ is constant and take any continuous function $f:Xtimes S^2tomathbb R^2$. Fix any point $x_0in X$ and using the Borsuk-Ulam Theorem, find a point $sin S^2$ such that $f(x_0,s)=f(x_0,-s)$.
By our assumption, for every $sin S^2$ the function $frestrictionXtimess$ is constant. So, for every $xin X$ we have
$$f(x,s)=f(x_0,s)=f(x_0,-s)=f(x,-s).$$
Remark. For examples of regular topological spaces on which all continuous real-valued functions are constant, see page 119 of Engelking's "General Topology".
$endgroup$
$begingroup$
Thank you very much for your attention to my question and your very interesting answer.
$endgroup$
– Ali Taghavi
Jan 4 at 20:53
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
return StackExchange.using("mathjaxEditing", function ()
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix)
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
);
);
, "mathjax-editing");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "504"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmathoverflow.net%2fquestions%2f320089%2fa-parametric-version-of-the-borsuk-ulam-theorem%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Theorem. For a topological space $X$ the following conditions are equivalent:
1) for any continuous map $f:Xtimes S^2tomathbb R^2$ there exists a point $sin S^2$ such that $f(x,s)=f(x,-s)$ for any $xin X$;
2) any continuous map $f:Xto mathbb R$ is constant.
Proof. (1) $Rightarrow$ (2) Assume that $X$ admits a non-constant map $hbar :Xto mathbb R$. We lose no generality assuming that $0,1subset hbar(X)subset[0,1]$.
Then there are points $x_0,x_1in X$ such that $hbar(x_i)=i$ for $iin0,1$.
Let $p:S^2tomathbb R^2$, $p:(x,y,z)mapsto (x,y)$, be the projection of the sphere $S^2=(x,y,z)inmathbb R^3:x^2+y^2+z^2=1$ onto the plane.
Let $varphi:S^2to S^2$ be any homeomorphism of the sphere $S^2$ such that $pcirc varphi(0,0,1)ne pcirc varphi(0,0,-1)$.
Using the Tietze-Urysohn Theorem, find a continuous map $psi:[0,1]times S^2tomathbb R^2$ such that $psi(0,s)=p(s)$ and $psi(1,x)=pcircvarphi(s)$ for all $sin S$. Then the continuous map $$f:Xtimes S^2tomathbb R^2,;;f:(x,s)mapsto psi(hbar(x),s),$$ has the following property:
if $f(x_0,s)=f(x_0,-s)$ for some $sin S^2$, then $sin(0,0,1),(0,0,-1)$ and $f(x_1,s)ne f(x_1,-s)$.
(2) $Rightarrow$ (1) Assume that each continuous map $Xtomathbb R$ is constant and take any continuous function $f:Xtimes S^2tomathbb R^2$. Fix any point $x_0in X$ and using the Borsuk-Ulam Theorem, find a point $sin S^2$ such that $f(x_0,s)=f(x_0,-s)$.
By our assumption, for every $sin S^2$ the function $frestrictionXtimess$ is constant. So, for every $xin X$ we have
$$f(x,s)=f(x_0,s)=f(x_0,-s)=f(x,-s).$$
Remark. For examples of regular topological spaces on which all continuous real-valued functions are constant, see page 119 of Engelking's "General Topology".
$endgroup$
$begingroup$
Thank you very much for your attention to my question and your very interesting answer.
$endgroup$
– Ali Taghavi
Jan 4 at 20:53
add a comment |
$begingroup$
Theorem. For a topological space $X$ the following conditions are equivalent:
1) for any continuous map $f:Xtimes S^2tomathbb R^2$ there exists a point $sin S^2$ such that $f(x,s)=f(x,-s)$ for any $xin X$;
2) any continuous map $f:Xto mathbb R$ is constant.
Proof. (1) $Rightarrow$ (2) Assume that $X$ admits a non-constant map $hbar :Xto mathbb R$. We lose no generality assuming that $0,1subset hbar(X)subset[0,1]$.
Then there are points $x_0,x_1in X$ such that $hbar(x_i)=i$ for $iin0,1$.
Let $p:S^2tomathbb R^2$, $p:(x,y,z)mapsto (x,y)$, be the projection of the sphere $S^2=(x,y,z)inmathbb R^3:x^2+y^2+z^2=1$ onto the plane.
Let $varphi:S^2to S^2$ be any homeomorphism of the sphere $S^2$ such that $pcirc varphi(0,0,1)ne pcirc varphi(0,0,-1)$.
Using the Tietze-Urysohn Theorem, find a continuous map $psi:[0,1]times S^2tomathbb R^2$ such that $psi(0,s)=p(s)$ and $psi(1,x)=pcircvarphi(s)$ for all $sin S$. Then the continuous map $$f:Xtimes S^2tomathbb R^2,;;f:(x,s)mapsto psi(hbar(x),s),$$ has the following property:
if $f(x_0,s)=f(x_0,-s)$ for some $sin S^2$, then $sin(0,0,1),(0,0,-1)$ and $f(x_1,s)ne f(x_1,-s)$.
(2) $Rightarrow$ (1) Assume that each continuous map $Xtomathbb R$ is constant and take any continuous function $f:Xtimes S^2tomathbb R^2$. Fix any point $x_0in X$ and using the Borsuk-Ulam Theorem, find a point $sin S^2$ such that $f(x_0,s)=f(x_0,-s)$.
By our assumption, for every $sin S^2$ the function $frestrictionXtimess$ is constant. So, for every $xin X$ we have
$$f(x,s)=f(x_0,s)=f(x_0,-s)=f(x,-s).$$
Remark. For examples of regular topological spaces on which all continuous real-valued functions are constant, see page 119 of Engelking's "General Topology".
$endgroup$
$begingroup$
Thank you very much for your attention to my question and your very interesting answer.
$endgroup$
– Ali Taghavi
Jan 4 at 20:53
add a comment |
$begingroup$
Theorem. For a topological space $X$ the following conditions are equivalent:
1) for any continuous map $f:Xtimes S^2tomathbb R^2$ there exists a point $sin S^2$ such that $f(x,s)=f(x,-s)$ for any $xin X$;
2) any continuous map $f:Xto mathbb R$ is constant.
Proof. (1) $Rightarrow$ (2) Assume that $X$ admits a non-constant map $hbar :Xto mathbb R$. We lose no generality assuming that $0,1subset hbar(X)subset[0,1]$.
Then there are points $x_0,x_1in X$ such that $hbar(x_i)=i$ for $iin0,1$.
Let $p:S^2tomathbb R^2$, $p:(x,y,z)mapsto (x,y)$, be the projection of the sphere $S^2=(x,y,z)inmathbb R^3:x^2+y^2+z^2=1$ onto the plane.
Let $varphi:S^2to S^2$ be any homeomorphism of the sphere $S^2$ such that $pcirc varphi(0,0,1)ne pcirc varphi(0,0,-1)$.
Using the Tietze-Urysohn Theorem, find a continuous map $psi:[0,1]times S^2tomathbb R^2$ such that $psi(0,s)=p(s)$ and $psi(1,x)=pcircvarphi(s)$ for all $sin S$. Then the continuous map $$f:Xtimes S^2tomathbb R^2,;;f:(x,s)mapsto psi(hbar(x),s),$$ has the following property:
if $f(x_0,s)=f(x_0,-s)$ for some $sin S^2$, then $sin(0,0,1),(0,0,-1)$ and $f(x_1,s)ne f(x_1,-s)$.
(2) $Rightarrow$ (1) Assume that each continuous map $Xtomathbb R$ is constant and take any continuous function $f:Xtimes S^2tomathbb R^2$. Fix any point $x_0in X$ and using the Borsuk-Ulam Theorem, find a point $sin S^2$ such that $f(x_0,s)=f(x_0,-s)$.
By our assumption, for every $sin S^2$ the function $frestrictionXtimess$ is constant. So, for every $xin X$ we have
$$f(x,s)=f(x_0,s)=f(x_0,-s)=f(x,-s).$$
Remark. For examples of regular topological spaces on which all continuous real-valued functions are constant, see page 119 of Engelking's "General Topology".
$endgroup$
Theorem. For a topological space $X$ the following conditions are equivalent:
1) for any continuous map $f:Xtimes S^2tomathbb R^2$ there exists a point $sin S^2$ such that $f(x,s)=f(x,-s)$ for any $xin X$;
2) any continuous map $f:Xto mathbb R$ is constant.
Proof. (1) $Rightarrow$ (2) Assume that $X$ admits a non-constant map $hbar :Xto mathbb R$. We lose no generality assuming that $0,1subset hbar(X)subset[0,1]$.
Then there are points $x_0,x_1in X$ such that $hbar(x_i)=i$ for $iin0,1$.
Let $p:S^2tomathbb R^2$, $p:(x,y,z)mapsto (x,y)$, be the projection of the sphere $S^2=(x,y,z)inmathbb R^3:x^2+y^2+z^2=1$ onto the plane.
Let $varphi:S^2to S^2$ be any homeomorphism of the sphere $S^2$ such that $pcirc varphi(0,0,1)ne pcirc varphi(0,0,-1)$.
Using the Tietze-Urysohn Theorem, find a continuous map $psi:[0,1]times S^2tomathbb R^2$ such that $psi(0,s)=p(s)$ and $psi(1,x)=pcircvarphi(s)$ for all $sin S$. Then the continuous map $$f:Xtimes S^2tomathbb R^2,;;f:(x,s)mapsto psi(hbar(x),s),$$ has the following property:
if $f(x_0,s)=f(x_0,-s)$ for some $sin S^2$, then $sin(0,0,1),(0,0,-1)$ and $f(x_1,s)ne f(x_1,-s)$.
(2) $Rightarrow$ (1) Assume that each continuous map $Xtomathbb R$ is constant and take any continuous function $f:Xtimes S^2tomathbb R^2$. Fix any point $x_0in X$ and using the Borsuk-Ulam Theorem, find a point $sin S^2$ such that $f(x_0,s)=f(x_0,-s)$.
By our assumption, for every $sin S^2$ the function $frestrictionXtimess$ is constant. So, for every $xin X$ we have
$$f(x,s)=f(x_0,s)=f(x_0,-s)=f(x,-s).$$
Remark. For examples of regular topological spaces on which all continuous real-valued functions are constant, see page 119 of Engelking's "General Topology".
edited Jan 4 at 19:56
answered Jan 4 at 19:49
Taras BanakhTaras Banakh
16.2k13291
16.2k13291
$begingroup$
Thank you very much for your attention to my question and your very interesting answer.
$endgroup$
– Ali Taghavi
Jan 4 at 20:53
add a comment |
$begingroup$
Thank you very much for your attention to my question and your very interesting answer.
$endgroup$
– Ali Taghavi
Jan 4 at 20:53
$begingroup$
Thank you very much for your attention to my question and your very interesting answer.
$endgroup$
– Ali Taghavi
Jan 4 at 20:53
$begingroup$
Thank you very much for your attention to my question and your very interesting answer.
$endgroup$
– Ali Taghavi
Jan 4 at 20:53
add a comment |
Thanks for contributing an answer to MathOverflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmathoverflow.net%2fquestions%2f320089%2fa-parametric-version-of-the-borsuk-ulam-theorem%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
3
$begingroup$
Who downvoted this? It's a totally reasonable question!
$endgroup$
– Dylan Wilson
Jan 4 at 18:08
$begingroup$
At least we may consider any set $X$ with the trivial topology:)
$endgroup$
– Aleksei Kulikov
Jan 4 at 18:17
3
$begingroup$
A less stringent condition would be that there is a continuous (instead of constant) map $tto x(t)$ with $f(t,x(t))=f(t,-x(t))$.
$endgroup$
– BS.
Jan 5 at 11:07