How to show that $phi vdash psi$ implies $phi^{mathbf{M}} vdash psi^{mathbf{M}}$
Given a class $mathbf{M} neq emptyset$ and a formula $phi$ from the language of set theory, let $phi^{mathbf{M}}$ denote the relativizatization of $phi$ to $mathbf{M}$. I want to show the if $phi vdash psi$, then $phi^{mathbf{M}} vdash psi^{mathbf{M}}$. I tried proving that if $vdash phi$, then $vdash phi^{mathbf{M}}$, but I'm getting stucked in the induction steps - and one of the induction steps seems to be exactly what I want to prove. Anyone can shed some light?
logic set-theory
add a comment |
Given a class $mathbf{M} neq emptyset$ and a formula $phi$ from the language of set theory, let $phi^{mathbf{M}}$ denote the relativizatization of $phi$ to $mathbf{M}$. I want to show the if $phi vdash psi$, then $phi^{mathbf{M}} vdash psi^{mathbf{M}}$. I tried proving that if $vdash phi$, then $vdash phi^{mathbf{M}}$, but I'm getting stucked in the induction steps - and one of the induction steps seems to be exactly what I want to prove. Anyone can shed some light?
logic set-theory
3
Show that your inference rules relativize, and then mechanically relativize the proof.
– Asaf Karagila♦
Dec 26 at 8:26
add a comment |
Given a class $mathbf{M} neq emptyset$ and a formula $phi$ from the language of set theory, let $phi^{mathbf{M}}$ denote the relativizatization of $phi$ to $mathbf{M}$. I want to show the if $phi vdash psi$, then $phi^{mathbf{M}} vdash psi^{mathbf{M}}$. I tried proving that if $vdash phi$, then $vdash phi^{mathbf{M}}$, but I'm getting stucked in the induction steps - and one of the induction steps seems to be exactly what I want to prove. Anyone can shed some light?
logic set-theory
Given a class $mathbf{M} neq emptyset$ and a formula $phi$ from the language of set theory, let $phi^{mathbf{M}}$ denote the relativizatization of $phi$ to $mathbf{M}$. I want to show the if $phi vdash psi$, then $phi^{mathbf{M}} vdash psi^{mathbf{M}}$. I tried proving that if $vdash phi$, then $vdash phi^{mathbf{M}}$, but I'm getting stucked in the induction steps - and one of the induction steps seems to be exactly what I want to prove. Anyone can shed some light?
logic set-theory
logic set-theory
asked Dec 26 at 6:32
Nuntractatuses Amável
61812
61812
3
Show that your inference rules relativize, and then mechanically relativize the proof.
– Asaf Karagila♦
Dec 26 at 8:26
add a comment |
3
Show that your inference rules relativize, and then mechanically relativize the proof.
– Asaf Karagila♦
Dec 26 at 8:26
3
3
Show that your inference rules relativize, and then mechanically relativize the proof.
– Asaf Karagila♦
Dec 26 at 8:26
Show that your inference rules relativize, and then mechanically relativize the proof.
– Asaf Karagila♦
Dec 26 at 8:26
add a comment |
1 Answer
1
active
oldest
votes
For any structure $A$ in the language of set theory, the class $mathbf{M}$ can be interpreted as a subset $mathbf{M}^A$ of $A$, which we view as a substructure of $A$ by restricting $in$ to $mathbf{M}^A$.
Then given a formula $varphi$, the defining property of the formula $varphi^mathbf{M}$ is that for any structure $A$, we have $Amodels varphi^mathbf{M}$ if and only if $mathbf{M}^Amodels varphi$.
Now suppose $varphivdash psi$. By soundness and completeness, we have $varphimodels psi$, and it suffices to show $varphi^mathbf{M}models psi^mathbf{M}$. So let $A$ be any model of $varphi^mathbf{M}$. Then $mathbf{M}^Amodels varphi$. Since $varphimodels psi$, we have $mathbf{M}^Amodels psi$, so $Amodels psi^mathbf{M}$.
nice. I was trying to do it without using $vDash$ - only the formal deductions. I would prefer to do it in this way, but it is just personal preference.
– Nuntractatuses Amável
Dec 26 at 6:47
I tried proving the defining property you mentioned, and I encountered some dificulties. Mainly, the point that if $phi$ is the sentence $exists x psi$, then $psi$ is not necessarily a sentence - in which case I am not sure what the defining property means. I then tried proving for arbitrary formulas, with an assignment of values for the variables: then it struck me that, for this to make any sense, the variables can only assume values in $mathbf{M}^A$. Is this the case? I've seen relativization only in the context of set theory - in Kunen's book. I'm slightly confused.
– Nuntractatuses Amável
Dec 26 at 8:07
2
Yes, to prove the "defining property", you need to do an induction over formulas. Here the statement you want to prove by induction is: For any formula $varphi(x)$, any structure $A$, and any tuple $ain (mathbf{M}^A)^x$, we have $Amodels varphi^{mathbf{M}}(a)$ if and only if $mathbf{M}^Amodels varphi(a)$. This restricts to the property I wrote above when $varphi$ is a sentence.
– Alex Kruckman
Dec 26 at 15:50
2
If you prefer a purely syntactic proof, you can follow Asaf's hint above.
– Alex Kruckman
Dec 26 at 15:52
I managed to prove it (the "defining property"), thank you :). I'll try to do it in a purely syntactical way, now.
– Nuntractatuses Amável
yesterday
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: "69"
};
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%2fmath.stackexchange.com%2fquestions%2f3052696%2fhow-to-show-that-phi-vdash-psi-implies-phi-mathbfm-vdash-psi-mat%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
For any structure $A$ in the language of set theory, the class $mathbf{M}$ can be interpreted as a subset $mathbf{M}^A$ of $A$, which we view as a substructure of $A$ by restricting $in$ to $mathbf{M}^A$.
Then given a formula $varphi$, the defining property of the formula $varphi^mathbf{M}$ is that for any structure $A$, we have $Amodels varphi^mathbf{M}$ if and only if $mathbf{M}^Amodels varphi$.
Now suppose $varphivdash psi$. By soundness and completeness, we have $varphimodels psi$, and it suffices to show $varphi^mathbf{M}models psi^mathbf{M}$. So let $A$ be any model of $varphi^mathbf{M}$. Then $mathbf{M}^Amodels varphi$. Since $varphimodels psi$, we have $mathbf{M}^Amodels psi$, so $Amodels psi^mathbf{M}$.
nice. I was trying to do it without using $vDash$ - only the formal deductions. I would prefer to do it in this way, but it is just personal preference.
– Nuntractatuses Amável
Dec 26 at 6:47
I tried proving the defining property you mentioned, and I encountered some dificulties. Mainly, the point that if $phi$ is the sentence $exists x psi$, then $psi$ is not necessarily a sentence - in which case I am not sure what the defining property means. I then tried proving for arbitrary formulas, with an assignment of values for the variables: then it struck me that, for this to make any sense, the variables can only assume values in $mathbf{M}^A$. Is this the case? I've seen relativization only in the context of set theory - in Kunen's book. I'm slightly confused.
– Nuntractatuses Amável
Dec 26 at 8:07
2
Yes, to prove the "defining property", you need to do an induction over formulas. Here the statement you want to prove by induction is: For any formula $varphi(x)$, any structure $A$, and any tuple $ain (mathbf{M}^A)^x$, we have $Amodels varphi^{mathbf{M}}(a)$ if and only if $mathbf{M}^Amodels varphi(a)$. This restricts to the property I wrote above when $varphi$ is a sentence.
– Alex Kruckman
Dec 26 at 15:50
2
If you prefer a purely syntactic proof, you can follow Asaf's hint above.
– Alex Kruckman
Dec 26 at 15:52
I managed to prove it (the "defining property"), thank you :). I'll try to do it in a purely syntactical way, now.
– Nuntractatuses Amável
yesterday
add a comment |
For any structure $A$ in the language of set theory, the class $mathbf{M}$ can be interpreted as a subset $mathbf{M}^A$ of $A$, which we view as a substructure of $A$ by restricting $in$ to $mathbf{M}^A$.
Then given a formula $varphi$, the defining property of the formula $varphi^mathbf{M}$ is that for any structure $A$, we have $Amodels varphi^mathbf{M}$ if and only if $mathbf{M}^Amodels varphi$.
Now suppose $varphivdash psi$. By soundness and completeness, we have $varphimodels psi$, and it suffices to show $varphi^mathbf{M}models psi^mathbf{M}$. So let $A$ be any model of $varphi^mathbf{M}$. Then $mathbf{M}^Amodels varphi$. Since $varphimodels psi$, we have $mathbf{M}^Amodels psi$, so $Amodels psi^mathbf{M}$.
nice. I was trying to do it without using $vDash$ - only the formal deductions. I would prefer to do it in this way, but it is just personal preference.
– Nuntractatuses Amável
Dec 26 at 6:47
I tried proving the defining property you mentioned, and I encountered some dificulties. Mainly, the point that if $phi$ is the sentence $exists x psi$, then $psi$ is not necessarily a sentence - in which case I am not sure what the defining property means. I then tried proving for arbitrary formulas, with an assignment of values for the variables: then it struck me that, for this to make any sense, the variables can only assume values in $mathbf{M}^A$. Is this the case? I've seen relativization only in the context of set theory - in Kunen's book. I'm slightly confused.
– Nuntractatuses Amável
Dec 26 at 8:07
2
Yes, to prove the "defining property", you need to do an induction over formulas. Here the statement you want to prove by induction is: For any formula $varphi(x)$, any structure $A$, and any tuple $ain (mathbf{M}^A)^x$, we have $Amodels varphi^{mathbf{M}}(a)$ if and only if $mathbf{M}^Amodels varphi(a)$. This restricts to the property I wrote above when $varphi$ is a sentence.
– Alex Kruckman
Dec 26 at 15:50
2
If you prefer a purely syntactic proof, you can follow Asaf's hint above.
– Alex Kruckman
Dec 26 at 15:52
I managed to prove it (the "defining property"), thank you :). I'll try to do it in a purely syntactical way, now.
– Nuntractatuses Amável
yesterday
add a comment |
For any structure $A$ in the language of set theory, the class $mathbf{M}$ can be interpreted as a subset $mathbf{M}^A$ of $A$, which we view as a substructure of $A$ by restricting $in$ to $mathbf{M}^A$.
Then given a formula $varphi$, the defining property of the formula $varphi^mathbf{M}$ is that for any structure $A$, we have $Amodels varphi^mathbf{M}$ if and only if $mathbf{M}^Amodels varphi$.
Now suppose $varphivdash psi$. By soundness and completeness, we have $varphimodels psi$, and it suffices to show $varphi^mathbf{M}models psi^mathbf{M}$. So let $A$ be any model of $varphi^mathbf{M}$. Then $mathbf{M}^Amodels varphi$. Since $varphimodels psi$, we have $mathbf{M}^Amodels psi$, so $Amodels psi^mathbf{M}$.
For any structure $A$ in the language of set theory, the class $mathbf{M}$ can be interpreted as a subset $mathbf{M}^A$ of $A$, which we view as a substructure of $A$ by restricting $in$ to $mathbf{M}^A$.
Then given a formula $varphi$, the defining property of the formula $varphi^mathbf{M}$ is that for any structure $A$, we have $Amodels varphi^mathbf{M}$ if and only if $mathbf{M}^Amodels varphi$.
Now suppose $varphivdash psi$. By soundness and completeness, we have $varphimodels psi$, and it suffices to show $varphi^mathbf{M}models psi^mathbf{M}$. So let $A$ be any model of $varphi^mathbf{M}$. Then $mathbf{M}^Amodels varphi$. Since $varphimodels psi$, we have $mathbf{M}^Amodels psi$, so $Amodels psi^mathbf{M}$.
answered Dec 26 at 6:43
Alex Kruckman
26.4k22555
26.4k22555
nice. I was trying to do it without using $vDash$ - only the formal deductions. I would prefer to do it in this way, but it is just personal preference.
– Nuntractatuses Amável
Dec 26 at 6:47
I tried proving the defining property you mentioned, and I encountered some dificulties. Mainly, the point that if $phi$ is the sentence $exists x psi$, then $psi$ is not necessarily a sentence - in which case I am not sure what the defining property means. I then tried proving for arbitrary formulas, with an assignment of values for the variables: then it struck me that, for this to make any sense, the variables can only assume values in $mathbf{M}^A$. Is this the case? I've seen relativization only in the context of set theory - in Kunen's book. I'm slightly confused.
– Nuntractatuses Amável
Dec 26 at 8:07
2
Yes, to prove the "defining property", you need to do an induction over formulas. Here the statement you want to prove by induction is: For any formula $varphi(x)$, any structure $A$, and any tuple $ain (mathbf{M}^A)^x$, we have $Amodels varphi^{mathbf{M}}(a)$ if and only if $mathbf{M}^Amodels varphi(a)$. This restricts to the property I wrote above when $varphi$ is a sentence.
– Alex Kruckman
Dec 26 at 15:50
2
If you prefer a purely syntactic proof, you can follow Asaf's hint above.
– Alex Kruckman
Dec 26 at 15:52
I managed to prove it (the "defining property"), thank you :). I'll try to do it in a purely syntactical way, now.
– Nuntractatuses Amável
yesterday
add a comment |
nice. I was trying to do it without using $vDash$ - only the formal deductions. I would prefer to do it in this way, but it is just personal preference.
– Nuntractatuses Amável
Dec 26 at 6:47
I tried proving the defining property you mentioned, and I encountered some dificulties. Mainly, the point that if $phi$ is the sentence $exists x psi$, then $psi$ is not necessarily a sentence - in which case I am not sure what the defining property means. I then tried proving for arbitrary formulas, with an assignment of values for the variables: then it struck me that, for this to make any sense, the variables can only assume values in $mathbf{M}^A$. Is this the case? I've seen relativization only in the context of set theory - in Kunen's book. I'm slightly confused.
– Nuntractatuses Amável
Dec 26 at 8:07
2
Yes, to prove the "defining property", you need to do an induction over formulas. Here the statement you want to prove by induction is: For any formula $varphi(x)$, any structure $A$, and any tuple $ain (mathbf{M}^A)^x$, we have $Amodels varphi^{mathbf{M}}(a)$ if and only if $mathbf{M}^Amodels varphi(a)$. This restricts to the property I wrote above when $varphi$ is a sentence.
– Alex Kruckman
Dec 26 at 15:50
2
If you prefer a purely syntactic proof, you can follow Asaf's hint above.
– Alex Kruckman
Dec 26 at 15:52
I managed to prove it (the "defining property"), thank you :). I'll try to do it in a purely syntactical way, now.
– Nuntractatuses Amável
yesterday
nice. I was trying to do it without using $vDash$ - only the formal deductions. I would prefer to do it in this way, but it is just personal preference.
– Nuntractatuses Amável
Dec 26 at 6:47
nice. I was trying to do it without using $vDash$ - only the formal deductions. I would prefer to do it in this way, but it is just personal preference.
– Nuntractatuses Amável
Dec 26 at 6:47
I tried proving the defining property you mentioned, and I encountered some dificulties. Mainly, the point that if $phi$ is the sentence $exists x psi$, then $psi$ is not necessarily a sentence - in which case I am not sure what the defining property means. I then tried proving for arbitrary formulas, with an assignment of values for the variables: then it struck me that, for this to make any sense, the variables can only assume values in $mathbf{M}^A$. Is this the case? I've seen relativization only in the context of set theory - in Kunen's book. I'm slightly confused.
– Nuntractatuses Amável
Dec 26 at 8:07
I tried proving the defining property you mentioned, and I encountered some dificulties. Mainly, the point that if $phi$ is the sentence $exists x psi$, then $psi$ is not necessarily a sentence - in which case I am not sure what the defining property means. I then tried proving for arbitrary formulas, with an assignment of values for the variables: then it struck me that, for this to make any sense, the variables can only assume values in $mathbf{M}^A$. Is this the case? I've seen relativization only in the context of set theory - in Kunen's book. I'm slightly confused.
– Nuntractatuses Amável
Dec 26 at 8:07
2
2
Yes, to prove the "defining property", you need to do an induction over formulas. Here the statement you want to prove by induction is: For any formula $varphi(x)$, any structure $A$, and any tuple $ain (mathbf{M}^A)^x$, we have $Amodels varphi^{mathbf{M}}(a)$ if and only if $mathbf{M}^Amodels varphi(a)$. This restricts to the property I wrote above when $varphi$ is a sentence.
– Alex Kruckman
Dec 26 at 15:50
Yes, to prove the "defining property", you need to do an induction over formulas. Here the statement you want to prove by induction is: For any formula $varphi(x)$, any structure $A$, and any tuple $ain (mathbf{M}^A)^x$, we have $Amodels varphi^{mathbf{M}}(a)$ if and only if $mathbf{M}^Amodels varphi(a)$. This restricts to the property I wrote above when $varphi$ is a sentence.
– Alex Kruckman
Dec 26 at 15:50
2
2
If you prefer a purely syntactic proof, you can follow Asaf's hint above.
– Alex Kruckman
Dec 26 at 15:52
If you prefer a purely syntactic proof, you can follow Asaf's hint above.
– Alex Kruckman
Dec 26 at 15:52
I managed to prove it (the "defining property"), thank you :). I'll try to do it in a purely syntactical way, now.
– Nuntractatuses Amável
yesterday
I managed to prove it (the "defining property"), thank you :). I'll try to do it in a purely syntactical way, now.
– Nuntractatuses Amável
yesterday
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- 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.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- 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.
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%2fmath.stackexchange.com%2fquestions%2f3052696%2fhow-to-show-that-phi-vdash-psi-implies-phi-mathbfm-vdash-psi-mat%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
Show that your inference rules relativize, and then mechanically relativize the proof.
– Asaf Karagila♦
Dec 26 at 8:26