Terminology about trees












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In set theory, a tree is usually defined as a partial order such that the set of elements below any given one is well-ordered. I am interested in the class of partial orders $P$ such that for every $p in P$, the set of $q leq p$ is just linearly ordered. Does this have a name?










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$endgroup$








  • 1




    $begingroup$
    rd.springer.com/article/10.1007/BF00571186
    $endgroup$
    – Asaf Karagila
    Jan 18 at 15:45






  • 1




    $begingroup$
    Prefix orders seem to be relevant, if for no other reason than they appear to fit the required definitional niche. See en.m.wikipedia.org/wiki/Prefix_order
    $endgroup$
    – Not Mike
    Jan 18 at 17:18












  • $begingroup$
    Thanks @NotMike! It's nice to see this coming from outside of pure set theory. Feel free to put this as an answer.
    $endgroup$
    – Monroe Eskew
    Jan 18 at 17:26










  • $begingroup$
    Adeleke and Neumann have a Memoir of the AMS 'Relations related to betweenness' which considers various structures along these lines. In particular, a partially ordered set satisfying the property above which is also assumed to be connected (every pair of elements has a common lower bound) is called a semilinearly ordered set. I don't know if they have a name for such objects if they're not connected.
    $endgroup$
    – shane.orourke
    Jan 18 at 19:22
















10












$begingroup$


In set theory, a tree is usually defined as a partial order such that the set of elements below any given one is well-ordered. I am interested in the class of partial orders $P$ such that for every $p in P$, the set of $q leq p$ is just linearly ordered. Does this have a name?










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    rd.springer.com/article/10.1007/BF00571186
    $endgroup$
    – Asaf Karagila
    Jan 18 at 15:45






  • 1




    $begingroup$
    Prefix orders seem to be relevant, if for no other reason than they appear to fit the required definitional niche. See en.m.wikipedia.org/wiki/Prefix_order
    $endgroup$
    – Not Mike
    Jan 18 at 17:18












  • $begingroup$
    Thanks @NotMike! It's nice to see this coming from outside of pure set theory. Feel free to put this as an answer.
    $endgroup$
    – Monroe Eskew
    Jan 18 at 17:26










  • $begingroup$
    Adeleke and Neumann have a Memoir of the AMS 'Relations related to betweenness' which considers various structures along these lines. In particular, a partially ordered set satisfying the property above which is also assumed to be connected (every pair of elements has a common lower bound) is called a semilinearly ordered set. I don't know if they have a name for such objects if they're not connected.
    $endgroup$
    – shane.orourke
    Jan 18 at 19:22














10












10








10


1



$begingroup$


In set theory, a tree is usually defined as a partial order such that the set of elements below any given one is well-ordered. I am interested in the class of partial orders $P$ such that for every $p in P$, the set of $q leq p$ is just linearly ordered. Does this have a name?










share|cite|improve this question











$endgroup$




In set theory, a tree is usually defined as a partial order such that the set of elements below any given one is well-ordered. I am interested in the class of partial orders $P$ such that for every $p in P$, the set of $q leq p$ is just linearly ordered. Does this have a name?







set-theory terminology posets trees






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share|cite|improve this question













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edited Jan 18 at 15:32







Monroe Eskew

















asked Jan 18 at 12:42









Monroe EskewMonroe Eskew

7,65012158




7,65012158








  • 1




    $begingroup$
    rd.springer.com/article/10.1007/BF00571186
    $endgroup$
    – Asaf Karagila
    Jan 18 at 15:45






  • 1




    $begingroup$
    Prefix orders seem to be relevant, if for no other reason than they appear to fit the required definitional niche. See en.m.wikipedia.org/wiki/Prefix_order
    $endgroup$
    – Not Mike
    Jan 18 at 17:18












  • $begingroup$
    Thanks @NotMike! It's nice to see this coming from outside of pure set theory. Feel free to put this as an answer.
    $endgroup$
    – Monroe Eskew
    Jan 18 at 17:26










  • $begingroup$
    Adeleke and Neumann have a Memoir of the AMS 'Relations related to betweenness' which considers various structures along these lines. In particular, a partially ordered set satisfying the property above which is also assumed to be connected (every pair of elements has a common lower bound) is called a semilinearly ordered set. I don't know if they have a name for such objects if they're not connected.
    $endgroup$
    – shane.orourke
    Jan 18 at 19:22














  • 1




    $begingroup$
    rd.springer.com/article/10.1007/BF00571186
    $endgroup$
    – Asaf Karagila
    Jan 18 at 15:45






  • 1




    $begingroup$
    Prefix orders seem to be relevant, if for no other reason than they appear to fit the required definitional niche. See en.m.wikipedia.org/wiki/Prefix_order
    $endgroup$
    – Not Mike
    Jan 18 at 17:18












  • $begingroup$
    Thanks @NotMike! It's nice to see this coming from outside of pure set theory. Feel free to put this as an answer.
    $endgroup$
    – Monroe Eskew
    Jan 18 at 17:26










  • $begingroup$
    Adeleke and Neumann have a Memoir of the AMS 'Relations related to betweenness' which considers various structures along these lines. In particular, a partially ordered set satisfying the property above which is also assumed to be connected (every pair of elements has a common lower bound) is called a semilinearly ordered set. I don't know if they have a name for such objects if they're not connected.
    $endgroup$
    – shane.orourke
    Jan 18 at 19:22








1




1




$begingroup$
rd.springer.com/article/10.1007/BF00571186
$endgroup$
– Asaf Karagila
Jan 18 at 15:45




$begingroup$
rd.springer.com/article/10.1007/BF00571186
$endgroup$
– Asaf Karagila
Jan 18 at 15:45




1




1




$begingroup$
Prefix orders seem to be relevant, if for no other reason than they appear to fit the required definitional niche. See en.m.wikipedia.org/wiki/Prefix_order
$endgroup$
– Not Mike
Jan 18 at 17:18






$begingroup$
Prefix orders seem to be relevant, if for no other reason than they appear to fit the required definitional niche. See en.m.wikipedia.org/wiki/Prefix_order
$endgroup$
– Not Mike
Jan 18 at 17:18














$begingroup$
Thanks @NotMike! It's nice to see this coming from outside of pure set theory. Feel free to put this as an answer.
$endgroup$
– Monroe Eskew
Jan 18 at 17:26




$begingroup$
Thanks @NotMike! It's nice to see this coming from outside of pure set theory. Feel free to put this as an answer.
$endgroup$
– Monroe Eskew
Jan 18 at 17:26












$begingroup$
Adeleke and Neumann have a Memoir of the AMS 'Relations related to betweenness' which considers various structures along these lines. In particular, a partially ordered set satisfying the property above which is also assumed to be connected (every pair of elements has a common lower bound) is called a semilinearly ordered set. I don't know if they have a name for such objects if they're not connected.
$endgroup$
– shane.orourke
Jan 18 at 19:22




$begingroup$
Adeleke and Neumann have a Memoir of the AMS 'Relations related to betweenness' which considers various structures along these lines. In particular, a partially ordered set satisfying the property above which is also assumed to be connected (every pair of elements has a common lower bound) is called a semilinearly ordered set. I don't know if they have a name for such objects if they're not connected.
$endgroup$
– shane.orourke
Jan 18 at 19:22










2 Answers
2






active

oldest

votes


















10












$begingroup$

They are also called trees.



In that terminology, trees of your first kind are known as the well-founded trees, since they are trees where the tree order is well-founded (and well-founded linear orders are the same as well-orders).



I think that the situation is that because set theorists are mainly interested in the well-founded case, the terminology evolved to drop the adjective from well-founded trees.



There are many competing definitions of tree in mathematics, not all equivalent. For graph-theorists, for example, a tree is a certain kind of cycle-free graph.






share|cite|improve this answer









$endgroup$









  • 1




    $begingroup$
    This is also what I thought off the top of my head, but Jech, Kunen, and Kanamori all put well-foundedness into the definition of a tree. Do you know of a reference the defines trees as the more general class?
    $endgroup$
    – Monroe Eskew
    Jan 18 at 15:32










  • $begingroup$
    Well, those are all set theory references, and so they use the set theory convention, which as we said is focused on the well-founded case. I've seen the linearly ordered version sometimes in talks, but I don't know a specific reference. And in truth, I think that the non-well-founded tree case is simply much less studied. For finite trees, however, saying linear is enough (for every finite order is well-founded), and one can definitely find that.
    $endgroup$
    – Joel David Hamkins
    Jan 18 at 17:12






  • 1




    $begingroup$
    I guess the complication also is that "well-founded tree" now means something else in set theory, where the tree is growing downward and has no infinite branches.
    $endgroup$
    – Joel David Hamkins
    Jan 18 at 17:58






  • 2




    $begingroup$
    For one reference: Keisler uses the linear order definition in his article "Models with tree structures". Full citation: H. Jerome Keisler. “Models with tree structures”. In: Proceedings of the Tarski Symposium (Proc. Sympos. Pure Math., Vol. XXV, Univ. California, Berkeley, Calif., 1971) . Amer. Math. Soc., Providence, R.I., 1974, pp. 331–348.
    $endgroup$
    – Kameryn Williams
    Jan 18 at 22:27












  • $begingroup$
    But set-theoreticians, who use the word "tree" to mean well-founded tree, must occasionally have to refer to the more general trees. What do they call them? If I use "tree" to mean a poset in which the predecessors of any element are well-ordered, then what should I call a poset in which the predecessors of any element are linearly ordered? I have some vague recollection of hearing them called "pseudotrees" or something like that.
    $endgroup$
    – bof
    1 hour ago





















3












$begingroup$

Upgraded from a comment:



After a little bit of searching, the notion of prefix order seems to be relevant; if for no other reason than that it appears to fit the required definitional niche.



(Also, it seemed worth pointing out the notion of prefix-order is precisely that of a "first-order tree".)






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    2 Answers
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    2 Answers
    2






    active

    oldest

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    active

    oldest

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    10












    $begingroup$

    They are also called trees.



    In that terminology, trees of your first kind are known as the well-founded trees, since they are trees where the tree order is well-founded (and well-founded linear orders are the same as well-orders).



    I think that the situation is that because set theorists are mainly interested in the well-founded case, the terminology evolved to drop the adjective from well-founded trees.



    There are many competing definitions of tree in mathematics, not all equivalent. For graph-theorists, for example, a tree is a certain kind of cycle-free graph.






    share|cite|improve this answer









    $endgroup$









    • 1




      $begingroup$
      This is also what I thought off the top of my head, but Jech, Kunen, and Kanamori all put well-foundedness into the definition of a tree. Do you know of a reference the defines trees as the more general class?
      $endgroup$
      – Monroe Eskew
      Jan 18 at 15:32










    • $begingroup$
      Well, those are all set theory references, and so they use the set theory convention, which as we said is focused on the well-founded case. I've seen the linearly ordered version sometimes in talks, but I don't know a specific reference. And in truth, I think that the non-well-founded tree case is simply much less studied. For finite trees, however, saying linear is enough (for every finite order is well-founded), and one can definitely find that.
      $endgroup$
      – Joel David Hamkins
      Jan 18 at 17:12






    • 1




      $begingroup$
      I guess the complication also is that "well-founded tree" now means something else in set theory, where the tree is growing downward and has no infinite branches.
      $endgroup$
      – Joel David Hamkins
      Jan 18 at 17:58






    • 2




      $begingroup$
      For one reference: Keisler uses the linear order definition in his article "Models with tree structures". Full citation: H. Jerome Keisler. “Models with tree structures”. In: Proceedings of the Tarski Symposium (Proc. Sympos. Pure Math., Vol. XXV, Univ. California, Berkeley, Calif., 1971) . Amer. Math. Soc., Providence, R.I., 1974, pp. 331–348.
      $endgroup$
      – Kameryn Williams
      Jan 18 at 22:27












    • $begingroup$
      But set-theoreticians, who use the word "tree" to mean well-founded tree, must occasionally have to refer to the more general trees. What do they call them? If I use "tree" to mean a poset in which the predecessors of any element are well-ordered, then what should I call a poset in which the predecessors of any element are linearly ordered? I have some vague recollection of hearing them called "pseudotrees" or something like that.
      $endgroup$
      – bof
      1 hour ago


















    10












    $begingroup$

    They are also called trees.



    In that terminology, trees of your first kind are known as the well-founded trees, since they are trees where the tree order is well-founded (and well-founded linear orders are the same as well-orders).



    I think that the situation is that because set theorists are mainly interested in the well-founded case, the terminology evolved to drop the adjective from well-founded trees.



    There are many competing definitions of tree in mathematics, not all equivalent. For graph-theorists, for example, a tree is a certain kind of cycle-free graph.






    share|cite|improve this answer









    $endgroup$









    • 1




      $begingroup$
      This is also what I thought off the top of my head, but Jech, Kunen, and Kanamori all put well-foundedness into the definition of a tree. Do you know of a reference the defines trees as the more general class?
      $endgroup$
      – Monroe Eskew
      Jan 18 at 15:32










    • $begingroup$
      Well, those are all set theory references, and so they use the set theory convention, which as we said is focused on the well-founded case. I've seen the linearly ordered version sometimes in talks, but I don't know a specific reference. And in truth, I think that the non-well-founded tree case is simply much less studied. For finite trees, however, saying linear is enough (for every finite order is well-founded), and one can definitely find that.
      $endgroup$
      – Joel David Hamkins
      Jan 18 at 17:12






    • 1




      $begingroup$
      I guess the complication also is that "well-founded tree" now means something else in set theory, where the tree is growing downward and has no infinite branches.
      $endgroup$
      – Joel David Hamkins
      Jan 18 at 17:58






    • 2




      $begingroup$
      For one reference: Keisler uses the linear order definition in his article "Models with tree structures". Full citation: H. Jerome Keisler. “Models with tree structures”. In: Proceedings of the Tarski Symposium (Proc. Sympos. Pure Math., Vol. XXV, Univ. California, Berkeley, Calif., 1971) . Amer. Math. Soc., Providence, R.I., 1974, pp. 331–348.
      $endgroup$
      – Kameryn Williams
      Jan 18 at 22:27












    • $begingroup$
      But set-theoreticians, who use the word "tree" to mean well-founded tree, must occasionally have to refer to the more general trees. What do they call them? If I use "tree" to mean a poset in which the predecessors of any element are well-ordered, then what should I call a poset in which the predecessors of any element are linearly ordered? I have some vague recollection of hearing them called "pseudotrees" or something like that.
      $endgroup$
      – bof
      1 hour ago
















    10












    10








    10





    $begingroup$

    They are also called trees.



    In that terminology, trees of your first kind are known as the well-founded trees, since they are trees where the tree order is well-founded (and well-founded linear orders are the same as well-orders).



    I think that the situation is that because set theorists are mainly interested in the well-founded case, the terminology evolved to drop the adjective from well-founded trees.



    There are many competing definitions of tree in mathematics, not all equivalent. For graph-theorists, for example, a tree is a certain kind of cycle-free graph.






    share|cite|improve this answer









    $endgroup$



    They are also called trees.



    In that terminology, trees of your first kind are known as the well-founded trees, since they are trees where the tree order is well-founded (and well-founded linear orders are the same as well-orders).



    I think that the situation is that because set theorists are mainly interested in the well-founded case, the terminology evolved to drop the adjective from well-founded trees.



    There are many competing definitions of tree in mathematics, not all equivalent. For graph-theorists, for example, a tree is a certain kind of cycle-free graph.







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    answered Jan 18 at 13:26









    Joel David HamkinsJoel David Hamkins

    164k25502870




    164k25502870








    • 1




      $begingroup$
      This is also what I thought off the top of my head, but Jech, Kunen, and Kanamori all put well-foundedness into the definition of a tree. Do you know of a reference the defines trees as the more general class?
      $endgroup$
      – Monroe Eskew
      Jan 18 at 15:32










    • $begingroup$
      Well, those are all set theory references, and so they use the set theory convention, which as we said is focused on the well-founded case. I've seen the linearly ordered version sometimes in talks, but I don't know a specific reference. And in truth, I think that the non-well-founded tree case is simply much less studied. For finite trees, however, saying linear is enough (for every finite order is well-founded), and one can definitely find that.
      $endgroup$
      – Joel David Hamkins
      Jan 18 at 17:12






    • 1




      $begingroup$
      I guess the complication also is that "well-founded tree" now means something else in set theory, where the tree is growing downward and has no infinite branches.
      $endgroup$
      – Joel David Hamkins
      Jan 18 at 17:58






    • 2




      $begingroup$
      For one reference: Keisler uses the linear order definition in his article "Models with tree structures". Full citation: H. Jerome Keisler. “Models with tree structures”. In: Proceedings of the Tarski Symposium (Proc. Sympos. Pure Math., Vol. XXV, Univ. California, Berkeley, Calif., 1971) . Amer. Math. Soc., Providence, R.I., 1974, pp. 331–348.
      $endgroup$
      – Kameryn Williams
      Jan 18 at 22:27












    • $begingroup$
      But set-theoreticians, who use the word "tree" to mean well-founded tree, must occasionally have to refer to the more general trees. What do they call them? If I use "tree" to mean a poset in which the predecessors of any element are well-ordered, then what should I call a poset in which the predecessors of any element are linearly ordered? I have some vague recollection of hearing them called "pseudotrees" or something like that.
      $endgroup$
      – bof
      1 hour ago
















    • 1




      $begingroup$
      This is also what I thought off the top of my head, but Jech, Kunen, and Kanamori all put well-foundedness into the definition of a tree. Do you know of a reference the defines trees as the more general class?
      $endgroup$
      – Monroe Eskew
      Jan 18 at 15:32










    • $begingroup$
      Well, those are all set theory references, and so they use the set theory convention, which as we said is focused on the well-founded case. I've seen the linearly ordered version sometimes in talks, but I don't know a specific reference. And in truth, I think that the non-well-founded tree case is simply much less studied. For finite trees, however, saying linear is enough (for every finite order is well-founded), and one can definitely find that.
      $endgroup$
      – Joel David Hamkins
      Jan 18 at 17:12






    • 1




      $begingroup$
      I guess the complication also is that "well-founded tree" now means something else in set theory, where the tree is growing downward and has no infinite branches.
      $endgroup$
      – Joel David Hamkins
      Jan 18 at 17:58






    • 2




      $begingroup$
      For one reference: Keisler uses the linear order definition in his article "Models with tree structures". Full citation: H. Jerome Keisler. “Models with tree structures”. In: Proceedings of the Tarski Symposium (Proc. Sympos. Pure Math., Vol. XXV, Univ. California, Berkeley, Calif., 1971) . Amer. Math. Soc., Providence, R.I., 1974, pp. 331–348.
      $endgroup$
      – Kameryn Williams
      Jan 18 at 22:27












    • $begingroup$
      But set-theoreticians, who use the word "tree" to mean well-founded tree, must occasionally have to refer to the more general trees. What do they call them? If I use "tree" to mean a poset in which the predecessors of any element are well-ordered, then what should I call a poset in which the predecessors of any element are linearly ordered? I have some vague recollection of hearing them called "pseudotrees" or something like that.
      $endgroup$
      – bof
      1 hour ago










    1




    1




    $begingroup$
    This is also what I thought off the top of my head, but Jech, Kunen, and Kanamori all put well-foundedness into the definition of a tree. Do you know of a reference the defines trees as the more general class?
    $endgroup$
    – Monroe Eskew
    Jan 18 at 15:32




    $begingroup$
    This is also what I thought off the top of my head, but Jech, Kunen, and Kanamori all put well-foundedness into the definition of a tree. Do you know of a reference the defines trees as the more general class?
    $endgroup$
    – Monroe Eskew
    Jan 18 at 15:32












    $begingroup$
    Well, those are all set theory references, and so they use the set theory convention, which as we said is focused on the well-founded case. I've seen the linearly ordered version sometimes in talks, but I don't know a specific reference. And in truth, I think that the non-well-founded tree case is simply much less studied. For finite trees, however, saying linear is enough (for every finite order is well-founded), and one can definitely find that.
    $endgroup$
    – Joel David Hamkins
    Jan 18 at 17:12




    $begingroup$
    Well, those are all set theory references, and so they use the set theory convention, which as we said is focused on the well-founded case. I've seen the linearly ordered version sometimes in talks, but I don't know a specific reference. And in truth, I think that the non-well-founded tree case is simply much less studied. For finite trees, however, saying linear is enough (for every finite order is well-founded), and one can definitely find that.
    $endgroup$
    – Joel David Hamkins
    Jan 18 at 17:12




    1




    1




    $begingroup$
    I guess the complication also is that "well-founded tree" now means something else in set theory, where the tree is growing downward and has no infinite branches.
    $endgroup$
    – Joel David Hamkins
    Jan 18 at 17:58




    $begingroup$
    I guess the complication also is that "well-founded tree" now means something else in set theory, where the tree is growing downward and has no infinite branches.
    $endgroup$
    – Joel David Hamkins
    Jan 18 at 17:58




    2




    2




    $begingroup$
    For one reference: Keisler uses the linear order definition in his article "Models with tree structures". Full citation: H. Jerome Keisler. “Models with tree structures”. In: Proceedings of the Tarski Symposium (Proc. Sympos. Pure Math., Vol. XXV, Univ. California, Berkeley, Calif., 1971) . Amer. Math. Soc., Providence, R.I., 1974, pp. 331–348.
    $endgroup$
    – Kameryn Williams
    Jan 18 at 22:27






    $begingroup$
    For one reference: Keisler uses the linear order definition in his article "Models with tree structures". Full citation: H. Jerome Keisler. “Models with tree structures”. In: Proceedings of the Tarski Symposium (Proc. Sympos. Pure Math., Vol. XXV, Univ. California, Berkeley, Calif., 1971) . Amer. Math. Soc., Providence, R.I., 1974, pp. 331–348.
    $endgroup$
    – Kameryn Williams
    Jan 18 at 22:27














    $begingroup$
    But set-theoreticians, who use the word "tree" to mean well-founded tree, must occasionally have to refer to the more general trees. What do they call them? If I use "tree" to mean a poset in which the predecessors of any element are well-ordered, then what should I call a poset in which the predecessors of any element are linearly ordered? I have some vague recollection of hearing them called "pseudotrees" or something like that.
    $endgroup$
    – bof
    1 hour ago






    $begingroup$
    But set-theoreticians, who use the word "tree" to mean well-founded tree, must occasionally have to refer to the more general trees. What do they call them? If I use "tree" to mean a poset in which the predecessors of any element are well-ordered, then what should I call a poset in which the predecessors of any element are linearly ordered? I have some vague recollection of hearing them called "pseudotrees" or something like that.
    $endgroup$
    – bof
    1 hour ago













    3












    $begingroup$

    Upgraded from a comment:



    After a little bit of searching, the notion of prefix order seems to be relevant; if for no other reason than that it appears to fit the required definitional niche.



    (Also, it seemed worth pointing out the notion of prefix-order is precisely that of a "first-order tree".)






    share|cite|improve this answer









    $endgroup$


















      3












      $begingroup$

      Upgraded from a comment:



      After a little bit of searching, the notion of prefix order seems to be relevant; if for no other reason than that it appears to fit the required definitional niche.



      (Also, it seemed worth pointing out the notion of prefix-order is precisely that of a "first-order tree".)






      share|cite|improve this answer









      $endgroup$
















        3












        3








        3





        $begingroup$

        Upgraded from a comment:



        After a little bit of searching, the notion of prefix order seems to be relevant; if for no other reason than that it appears to fit the required definitional niche.



        (Also, it seemed worth pointing out the notion of prefix-order is precisely that of a "first-order tree".)






        share|cite|improve this answer









        $endgroup$



        Upgraded from a comment:



        After a little bit of searching, the notion of prefix order seems to be relevant; if for no other reason than that it appears to fit the required definitional niche.



        (Also, it seemed worth pointing out the notion of prefix-order is precisely that of a "first-order tree".)







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Jan 18 at 19:19









        Not MikeNot Mike

        1,3651528




        1,3651528






























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