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Improved exposition.
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Joel David Hamkins
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Yes, you could use the term lexicalThe lexical order here. Usually, if one hasof a well-ordered ordered list of orders $P_\alpha$, then one may define$\langle X_\alpha,\leq_\alpha\rangle$ is the lexical order on the product of the underlying space by$\Pi_\alpha X_\alpha$ placing $\vec x$$s$ before $\vec y$$t$ if $s_\alpha\lt_\alpha t_\alpha$ on the firstleast difference $x_\alpha$ is before $y_\alpha$ in $P_\alpha$coordinate. In

But this is not your casesituation, you don't havesince all your orders, but merely pre-orders live on the same set (since twothe set of sheep could have the same age, etc.).

But in your case, and you don't wantseek an order on that set, not on the product spaceset. That is, since you want to order the individual sheep, not sequences of sheep. All your orders have the same underlying set (the set of sheep), and so this isn't the usual meaning ofBut if you simply restrict the lexical order. One way to the constant sequences, you get what you want, and for this reason, I think about it is that you are restrictingfine to call it the lexical order to the constant sequences.

If $P_\alpha$Another difference is that you don't actually have orders, but pre-orders, since two sheep can have the same age, and so on. In this general setting, you have a set $X$ with a well-ordered seqeuncesequence of pre-orders on a set $X$$\leq_\alpha$, we mayand you define the order on $X$ by placing $x$ before $y$$a\leq b$ if the least index $\alpha$ where theyfor which $a$ and $b$ are not equivalent has $x$ before(if any such $y$ in$\alpha$ exists) has $P_\alpha$$a\lt_\alpha b$.

It is important that the setlist of orders is well-ordered, since otherwise there may be no such least difference coordinate $\alpha$, and the idea will run aground. But any finite list of criteria is of course well-ordered, as is any $\omega$-sequence of orders.

Yes, you could use the term lexical order here. Usually, if one has a well-ordered list of orders $P_\alpha$, then one may define the lexical order on the product of the underlying space by placing $\vec x$ before $\vec y$ if the first difference $x_\alpha$ is before $y_\alpha$ in $P_\alpha$. In your case, you don't have orders, but merely pre-orders (since two sheep could have the same age, etc.).

But in your case, you don't want the product space, since you want to order the individual sheep, not sequences of sheep. All your orders have the same underlying set (the set of sheep), and so this isn't the usual meaning of the lexical order. One way to think about it is that you are restricting the lexical order to the constant sequences.

If $P_\alpha$ is a well-ordered seqeunce of pre-orders on a set $X$, we may define the order on $X$ by placing $x$ before $y$ if the least $\alpha$ where they are not equivalent has $x$ before $y$ in $P_\alpha$.

It is important that the set of orders is well-ordered, since otherwise there may be no such least difference coordinate $\alpha$, and the idea will run aground.

The lexical order of a well ordered list of orders $\langle X_\alpha,\leq_\alpha\rangle$ is the order on the product space $\Pi_\alpha X_\alpha$ placing $s$ before $t$ if $s_\alpha\lt_\alpha t_\alpha$ on the least difference coordinate.

But this is not your situation, since all your orders live on the same set (the set of sheep), and you seek an order on that set, not on the product set. That is, you want to order the sheep, not sequences of sheep. But if you simply restrict the lexical order to the constant sequences, you get what you want, and for this reason, I think it is fine to call it the lexical order.

Another difference is that you don't actually have orders, but pre-orders, since two sheep can have the same age, and so on. In this general setting, you have a set $X$ with a well-ordered sequence of pre-orders $\leq_\alpha$, and you define $a\leq b$ if the least index $\alpha$ for which $a$ and $b$ are not equivalent (if any such $\alpha$ exists) has $a\lt_\alpha b$.

It is important that the list of orders is well-ordered, since otherwise there may be no such least difference coordinate $\alpha$, and the idea will run aground. But any finite list of criteria is of course well-ordered, as is any $\omega$-sequence of orders.

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Joel David Hamkins
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Yes, you could use the term lexical order here. Usually, if one has a well-ordered list of orders $P_\alpha$, then one may define the lexical order on the product of the underlying space by placing $\vec x$ before $\vec y$ if the first difference $x_\alpha$ is before $y_\alpha$ in $P_\alpha$. In your case, you don't have orders, but merely pre-orders (since two sheep could have the same age, etc.).

But alsoin your case, you don't want the product space, since you want to order the individual sheep, not sequences of sheep. All your orders have the same underlying set in each case (the set of sheep), and so this isn't the usual meaning of the lexical order. One way to think about it is that you don't wantare restricting the lexical order to look at the product space, but only at individual sheepconstant sequences.

If $P_\alpha$ is a well-ordered seqeunce of pre-orders on a set $X$, we may define the order on $X$ by placing $x$ before $y$ if the least $\alpha$ where they are not equivalent has $x$ before $y$ in $P_\alpha$.

It is important that the set of orders is well-ordered, since otherwise there may be no such least difference coordinate $\alpha$, and the idea will run aground.

Yes, you could use the term lexical order here. Usually, if one has a well-ordered list of orders $P_\alpha$, then one may define the lexical order on the product of the underlying space by placing $\vec x$ before $\vec y$ if the first difference $x_\alpha$ is before $y_\alpha$ in $P_\alpha$. In your case, you don't have orders, but merely pre-orders (since two sheep could have the same age, etc.).

But also, you have the same underlying set in each case (the set of sheep), and so you don't want to look at the product space, but only at individual sheep, placing $x$ before $y$ if the least $\alpha$ where they are not equivalent has $x$ before $y$ in $P_\alpha$.

Yes, you could use the term lexical order here. Usually, if one has a well-ordered list of orders $P_\alpha$, then one may define the lexical order on the product of the underlying space by placing $\vec x$ before $\vec y$ if the first difference $x_\alpha$ is before $y_\alpha$ in $P_\alpha$. In your case, you don't have orders, but merely pre-orders (since two sheep could have the same age, etc.).

But in your case, you don't want the product space, since you want to order the individual sheep, not sequences of sheep. All your orders have the same underlying set (the set of sheep), and so this isn't the usual meaning of the lexical order. One way to think about it is that you are restricting the lexical order to the constant sequences.

If $P_\alpha$ is a well-ordered seqeunce of pre-orders on a set $X$, we may define the order on $X$ by placing $x$ before $y$ if the least $\alpha$ where they are not equivalent has $x$ before $y$ in $P_\alpha$.

It is important that the set of orders is well-ordered, since otherwise there may be no such least difference coordinate $\alpha$, and the idea will run aground.

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Joel David Hamkins
  • 236.5k
  • 44
  • 777
  • 1.4k

Yes, you could use the term lexical order here. Usually, if one has a well-ordered list of orders $P_\alpha$, then one may define the lexical order on the product of the underlying space by placing $\vec x$ before $\vec y$ if the first difference $x_\alpha$ is before $y_\alpha$ in $P_\alpha$. In your case, you don't have orders, but merely pre-orders (since two sheep could have the same age, etc.).

But also, you have the same underlying set in each case (the set of sheep), and so you don't want to look at the product space, but only at individual sheep, placing $x$ before $y$ if the least $\alpha$ where they are not equivalent has $x$ before $y$ in $P_\alpha$.