Are these formal formulas equivalent?
Clash Royale CLAN TAG#URR8PPP
up vote
7
down vote
favorite
My textbook gave the following
$ forall x_0 (exists x_1 x_0=(mathbfO'' cdot x_1) vee exists x_1 x_0=((mathbfO'' cdot x_1)+mathbfO')) $,
then commented on the syntax and why the brackets are so important here, etc...
However, for this example, I gave
$ forall x_0 exists x_1 ( x_0=(mathbfO'' cdot x_1) vee x_0=(mathbfO'' cdot x_1)+mathbfO') $.
To me these are equivalent, but my text didn't mention this form and didn't necessarily suggest it's equivalent to the first.
So are they equivalent or the way I'm using $ exists x_1 $ gives my formula a different meaning?
Thanks
Edit
In other words, can the existential quantifier be "factored" like I did?
logic first-order-logic predicate-logic
add a comment |Â
up vote
7
down vote
favorite
My textbook gave the following
$ forall x_0 (exists x_1 x_0=(mathbfO'' cdot x_1) vee exists x_1 x_0=((mathbfO'' cdot x_1)+mathbfO')) $,
then commented on the syntax and why the brackets are so important here, etc...
However, for this example, I gave
$ forall x_0 exists x_1 ( x_0=(mathbfO'' cdot x_1) vee x_0=(mathbfO'' cdot x_1)+mathbfO') $.
To me these are equivalent, but my text didn't mention this form and didn't necessarily suggest it's equivalent to the first.
So are they equivalent or the way I'm using $ exists x_1 $ gives my formula a different meaning?
Thanks
Edit
In other words, can the existential quantifier be "factored" like I did?
logic first-order-logic predicate-logic
add a comment |Â
up vote
7
down vote
favorite
up vote
7
down vote
favorite
My textbook gave the following
$ forall x_0 (exists x_1 x_0=(mathbfO'' cdot x_1) vee exists x_1 x_0=((mathbfO'' cdot x_1)+mathbfO')) $,
then commented on the syntax and why the brackets are so important here, etc...
However, for this example, I gave
$ forall x_0 exists x_1 ( x_0=(mathbfO'' cdot x_1) vee x_0=(mathbfO'' cdot x_1)+mathbfO') $.
To me these are equivalent, but my text didn't mention this form and didn't necessarily suggest it's equivalent to the first.
So are they equivalent or the way I'm using $ exists x_1 $ gives my formula a different meaning?
Thanks
Edit
In other words, can the existential quantifier be "factored" like I did?
logic first-order-logic predicate-logic
My textbook gave the following
$ forall x_0 (exists x_1 x_0=(mathbfO'' cdot x_1) vee exists x_1 x_0=((mathbfO'' cdot x_1)+mathbfO')) $,
then commented on the syntax and why the brackets are so important here, etc...
However, for this example, I gave
$ forall x_0 exists x_1 ( x_0=(mathbfO'' cdot x_1) vee x_0=(mathbfO'' cdot x_1)+mathbfO') $.
To me these are equivalent, but my text didn't mention this form and didn't necessarily suggest it's equivalent to the first.
So are they equivalent or the way I'm using $ exists x_1 $ gives my formula a different meaning?
Thanks
Edit
In other words, can the existential quantifier be "factored" like I did?
logic first-order-logic predicate-logic
edited Aug 8 at 2:38
Henning Makholm
227k16292521
227k16292521
asked Aug 7 at 20:50
Stephen
1,2131819
1,2131819
add a comment |Â
add a comment |Â
2 Answers
2
active
oldest
votes
up vote
10
down vote
accepted
The claim that either there is some object that is $P$ or there is some object that is $Q$, $exists x_1 P(x_1) lor exists x_1 Q(x_1)$, is logically equivalent to the claim that there is some object that is either $P$ or $Q$, $exists x_1 (P(x_1) lor Q(x_1))$:
$exists x_1 P(x_1) lor exists x_1 Q(x_1) iff exists x_1 (P(x_1) lor Q(x_1))$.
Notice the same is not true for existential quantification with conjunction. For example, there exists a cat and there exists a dog, $exists x textCat(x) land exists x textDog(x)$, but this does not exactly mean there exists something which is both a cat and a dog, $exists x (textCat(x) land textDog(x))$.
As a caveat to the preceding image, it would be true to say that all objects are both a cat and a dog, $forall x (textCat(x) land textDog(x))$, if and only if all objects are a cat and all objects are a dog, $forall x textCat(x) land forall x textDog(x).$
1
One fine day with a woof and a purr
â Git Gud
Aug 8 at 8:37
add a comment |Â
up vote
10
down vote
The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.
1
Great article, thanks.
â Stephen
Aug 7 at 21:01
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
10
down vote
accepted
The claim that either there is some object that is $P$ or there is some object that is $Q$, $exists x_1 P(x_1) lor exists x_1 Q(x_1)$, is logically equivalent to the claim that there is some object that is either $P$ or $Q$, $exists x_1 (P(x_1) lor Q(x_1))$:
$exists x_1 P(x_1) lor exists x_1 Q(x_1) iff exists x_1 (P(x_1) lor Q(x_1))$.
Notice the same is not true for existential quantification with conjunction. For example, there exists a cat and there exists a dog, $exists x textCat(x) land exists x textDog(x)$, but this does not exactly mean there exists something which is both a cat and a dog, $exists x (textCat(x) land textDog(x))$.
As a caveat to the preceding image, it would be true to say that all objects are both a cat and a dog, $forall x (textCat(x) land textDog(x))$, if and only if all objects are a cat and all objects are a dog, $forall x textCat(x) land forall x textDog(x).$
1
One fine day with a woof and a purr
â Git Gud
Aug 8 at 8:37
add a comment |Â
up vote
10
down vote
accepted
The claim that either there is some object that is $P$ or there is some object that is $Q$, $exists x_1 P(x_1) lor exists x_1 Q(x_1)$, is logically equivalent to the claim that there is some object that is either $P$ or $Q$, $exists x_1 (P(x_1) lor Q(x_1))$:
$exists x_1 P(x_1) lor exists x_1 Q(x_1) iff exists x_1 (P(x_1) lor Q(x_1))$.
Notice the same is not true for existential quantification with conjunction. For example, there exists a cat and there exists a dog, $exists x textCat(x) land exists x textDog(x)$, but this does not exactly mean there exists something which is both a cat and a dog, $exists x (textCat(x) land textDog(x))$.
As a caveat to the preceding image, it would be true to say that all objects are both a cat and a dog, $forall x (textCat(x) land textDog(x))$, if and only if all objects are a cat and all objects are a dog, $forall x textCat(x) land forall x textDog(x).$
1
One fine day with a woof and a purr
â Git Gud
Aug 8 at 8:37
add a comment |Â
up vote
10
down vote
accepted
up vote
10
down vote
accepted
The claim that either there is some object that is $P$ or there is some object that is $Q$, $exists x_1 P(x_1) lor exists x_1 Q(x_1)$, is logically equivalent to the claim that there is some object that is either $P$ or $Q$, $exists x_1 (P(x_1) lor Q(x_1))$:
$exists x_1 P(x_1) lor exists x_1 Q(x_1) iff exists x_1 (P(x_1) lor Q(x_1))$.
Notice the same is not true for existential quantification with conjunction. For example, there exists a cat and there exists a dog, $exists x textCat(x) land exists x textDog(x)$, but this does not exactly mean there exists something which is both a cat and a dog, $exists x (textCat(x) land textDog(x))$.
As a caveat to the preceding image, it would be true to say that all objects are both a cat and a dog, $forall x (textCat(x) land textDog(x))$, if and only if all objects are a cat and all objects are a dog, $forall x textCat(x) land forall x textDog(x).$
The claim that either there is some object that is $P$ or there is some object that is $Q$, $exists x_1 P(x_1) lor exists x_1 Q(x_1)$, is logically equivalent to the claim that there is some object that is either $P$ or $Q$, $exists x_1 (P(x_1) lor Q(x_1))$:
$exists x_1 P(x_1) lor exists x_1 Q(x_1) iff exists x_1 (P(x_1) lor Q(x_1))$.
Notice the same is not true for existential quantification with conjunction. For example, there exists a cat and there exists a dog, $exists x textCat(x) land exists x textDog(x)$, but this does not exactly mean there exists something which is both a cat and a dog, $exists x (textCat(x) land textDog(x))$.
As a caveat to the preceding image, it would be true to say that all objects are both a cat and a dog, $forall x (textCat(x) land textDog(x))$, if and only if all objects are a cat and all objects are a dog, $forall x textCat(x) land forall x textDog(x).$
edited Aug 8 at 8:25
answered Aug 7 at 21:19
Matt A Pelto
1,709419
1,709419
1
One fine day with a woof and a purr
â Git Gud
Aug 8 at 8:37
add a comment |Â
1
One fine day with a woof and a purr
â Git Gud
Aug 8 at 8:37
1
1
One fine day with a woof and a purr
â Git Gud
Aug 8 at 8:37
One fine day with a woof and a purr
â Git Gud
Aug 8 at 8:37
add a comment |Â
up vote
10
down vote
The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.
1
Great article, thanks.
â Stephen
Aug 7 at 21:01
add a comment |Â
up vote
10
down vote
The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.
1
Great article, thanks.
â Stephen
Aug 7 at 21:01
add a comment |Â
up vote
10
down vote
up vote
10
down vote
The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.
The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.
answered Aug 7 at 20:58
mathcounterexamples.net
24.6k21653
24.6k21653
1
Great article, thanks.
â Stephen
Aug 7 at 21:01
add a comment |Â
1
Great article, thanks.
â Stephen
Aug 7 at 21:01
1
1
Great article, thanks.
â Stephen
Aug 7 at 21:01
Great article, thanks.
â Stephen
Aug 7 at 21:01
add a comment |Â
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
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f2875389%2fare-these-formal-formulas-equivalent%23new-answer', 'question_page');
);
Post as a guest
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
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
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