Are these formal formulas equivalent?

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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?







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    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?







    share|cite|improve this question























      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?







      share|cite|improve this question













      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?









      share|cite|improve this question












      share|cite|improve this question




      share|cite|improve this question








      edited Aug 8 at 2:38









      Henning Makholm

      227k16292521




      227k16292521









      asked Aug 7 at 20:50









      Stephen

      1,2131819




      1,2131819




















          2 Answers
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          active

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          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, $exists x (textCat(x) land textDog(x))$.



          enter image description here



          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, $forall x textCat(x) land forall x textDog(x).$






          share|cite|improve this answer



















          • 1




            One fine day with a woof and a purr
            – Git Gud
            Aug 8 at 8:37

















          up vote
          10
          down vote













          The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.






          share|cite|improve this answer

















          • 1




            Great article, thanks.
            – Stephen
            Aug 7 at 21:01










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          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, $exists x (textCat(x) land textDog(x))$.



          enter image description here



          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, $forall x textCat(x) land forall x textDog(x).$






          share|cite|improve this answer



















          • 1




            One fine day with a woof and a purr
            – Git Gud
            Aug 8 at 8:37














          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, $exists x (textCat(x) land textDog(x))$.



          enter image description here



          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, $forall x textCat(x) land forall x textDog(x).$






          share|cite|improve this answer



















          • 1




            One fine day with a woof and a purr
            – Git Gud
            Aug 8 at 8:37












          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, $exists x (textCat(x) land textDog(x))$.



          enter image description here



          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, $forall x textCat(x) land forall x textDog(x).$






          share|cite|improve this answer















          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, $exists x (textCat(x) land textDog(x))$.



          enter image description here



          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, $forall x textCat(x) land forall x textDog(x).$







          share|cite|improve this answer















          share|cite|improve this answer



          share|cite|improve this answer








          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
            – Git Gud
            Aug 8 at 8:37












          • 1




            One fine day with a woof and a purr
            – Git Gud
            Aug 8 at 8:37







          1




          1




          One fine day with a woof and a purr
          – Git Gud
          Aug 8 at 8:37




          One fine day with a woof and a purr
          – Git Gud
          Aug 8 at 8:37










          up vote
          10
          down vote













          The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.






          share|cite|improve this answer

















          • 1




            Great article, thanks.
            – Stephen
            Aug 7 at 21:01














          up vote
          10
          down vote













          The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.






          share|cite|improve this answer

















          • 1




            Great article, thanks.
            – Stephen
            Aug 7 at 21:01












          up vote
          10
          down vote










          up vote
          10
          down vote









          The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.






          share|cite|improve this answer













          The existential quantifier distributes over disjunction. So the two sentences are indeed logically equivalent.







          share|cite|improve this answer













          share|cite|improve this answer



          share|cite|improve this answer











          answered Aug 7 at 20:58









          mathcounterexamples.net

          24.6k21653




          24.6k21653







          • 1




            Great article, thanks.
            – Stephen
            Aug 7 at 21:01












          • 1




            Great article, thanks.
            – Stephen
            Aug 7 at 21:01







          1




          1




          Great article, thanks.
          – Stephen
          Aug 7 at 21:01




          Great article, thanks.
          – Stephen
          Aug 7 at 21:01












           

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