Ordinal multiplication












0














I understand why $(omega+1)cdot2 = omegacdot2+1$ and why $(omega+1)cdotomega = omega^2$



What I am struggling with is something along the lines of:



$(omegacdot3+4)cdot3$ which I think is = $omegacdot9+4$



And:



$(omegacdot3+4)(omegacdot3)$ which I think is = $omega^2cdot9$



Am I correct?










share|cite|improve this question
























  • Could you explain how to evaluate them?
    – Hanul Jeon
    Nov 25 at 5:08










  • (w.3 + 4).3 = (w.3 + 4) + (w.3 + 4) + (w.3 + 4) = w.3 + (4 + w.3) + (4 + w.3) + 4 = w.3 + w.3 + w.3 + 4 = w.9 + 4 ??
    – Fraiku
    Nov 25 at 9:22












  • Your first evaluation is correct; however the second one is not valid.
    – Hanul Jeon
    Nov 25 at 9:27










  • Thank you. I was following this explanation for (w + 1).w^2 and trying to extrapolate, but I'm not sure where I've gone wrong. Can you clarify?
    – Fraiku
    Nov 25 at 9:41


















0














I understand why $(omega+1)cdot2 = omegacdot2+1$ and why $(omega+1)cdotomega = omega^2$



What I am struggling with is something along the lines of:



$(omegacdot3+4)cdot3$ which I think is = $omegacdot9+4$



And:



$(omegacdot3+4)(omegacdot3)$ which I think is = $omega^2cdot9$



Am I correct?










share|cite|improve this question
























  • Could you explain how to evaluate them?
    – Hanul Jeon
    Nov 25 at 5:08










  • (w.3 + 4).3 = (w.3 + 4) + (w.3 + 4) + (w.3 + 4) = w.3 + (4 + w.3) + (4 + w.3) + 4 = w.3 + w.3 + w.3 + 4 = w.9 + 4 ??
    – Fraiku
    Nov 25 at 9:22












  • Your first evaluation is correct; however the second one is not valid.
    – Hanul Jeon
    Nov 25 at 9:27










  • Thank you. I was following this explanation for (w + 1).w^2 and trying to extrapolate, but I'm not sure where I've gone wrong. Can you clarify?
    – Fraiku
    Nov 25 at 9:41
















0












0








0







I understand why $(omega+1)cdot2 = omegacdot2+1$ and why $(omega+1)cdotomega = omega^2$



What I am struggling with is something along the lines of:



$(omegacdot3+4)cdot3$ which I think is = $omegacdot9+4$



And:



$(omegacdot3+4)(omegacdot3)$ which I think is = $omega^2cdot9$



Am I correct?










share|cite|improve this question















I understand why $(omega+1)cdot2 = omegacdot2+1$ and why $(omega+1)cdotomega = omega^2$



What I am struggling with is something along the lines of:



$(omegacdot3+4)cdot3$ which I think is = $omegacdot9+4$



And:



$(omegacdot3+4)(omegacdot3)$ which I think is = $omega^2cdot9$



Am I correct?







elementary-set-theory ordinals






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Nov 25 at 10:15









Holo

5,3372929




5,3372929










asked Nov 24 at 21:41









Fraiku

102




102












  • Could you explain how to evaluate them?
    – Hanul Jeon
    Nov 25 at 5:08










  • (w.3 + 4).3 = (w.3 + 4) + (w.3 + 4) + (w.3 + 4) = w.3 + (4 + w.3) + (4 + w.3) + 4 = w.3 + w.3 + w.3 + 4 = w.9 + 4 ??
    – Fraiku
    Nov 25 at 9:22












  • Your first evaluation is correct; however the second one is not valid.
    – Hanul Jeon
    Nov 25 at 9:27










  • Thank you. I was following this explanation for (w + 1).w^2 and trying to extrapolate, but I'm not sure where I've gone wrong. Can you clarify?
    – Fraiku
    Nov 25 at 9:41




















  • Could you explain how to evaluate them?
    – Hanul Jeon
    Nov 25 at 5:08










  • (w.3 + 4).3 = (w.3 + 4) + (w.3 + 4) + (w.3 + 4) = w.3 + (4 + w.3) + (4 + w.3) + 4 = w.3 + w.3 + w.3 + 4 = w.9 + 4 ??
    – Fraiku
    Nov 25 at 9:22












  • Your first evaluation is correct; however the second one is not valid.
    – Hanul Jeon
    Nov 25 at 9:27










  • Thank you. I was following this explanation for (w + 1).w^2 and trying to extrapolate, but I'm not sure where I've gone wrong. Can you clarify?
    – Fraiku
    Nov 25 at 9:41


















Could you explain how to evaluate them?
– Hanul Jeon
Nov 25 at 5:08




Could you explain how to evaluate them?
– Hanul Jeon
Nov 25 at 5:08












(w.3 + 4).3 = (w.3 + 4) + (w.3 + 4) + (w.3 + 4) = w.3 + (4 + w.3) + (4 + w.3) + 4 = w.3 + w.3 + w.3 + 4 = w.9 + 4 ??
– Fraiku
Nov 25 at 9:22






(w.3 + 4).3 = (w.3 + 4) + (w.3 + 4) + (w.3 + 4) = w.3 + (4 + w.3) + (4 + w.3) + 4 = w.3 + w.3 + w.3 + 4 = w.9 + 4 ??
– Fraiku
Nov 25 at 9:22














Your first evaluation is correct; however the second one is not valid.
– Hanul Jeon
Nov 25 at 9:27




Your first evaluation is correct; however the second one is not valid.
– Hanul Jeon
Nov 25 at 9:27












Thank you. I was following this explanation for (w + 1).w^2 and trying to extrapolate, but I'm not sure where I've gone wrong. Can you clarify?
– Fraiku
Nov 25 at 9:41






Thank you. I was following this explanation for (w + 1).w^2 and trying to extrapolate, but I'm not sure where I've gone wrong. Can you clarify?
– Fraiku
Nov 25 at 9:41












1 Answer
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oldest

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0














You have evaluated $(omegacdot 3+4)cdot 3$ correctly. However, $(omegacdot 3+4)cdot(omegacdot 3)$ is not correctly evaluated. I do not know which step of your evaluation is incorrect, but I guess you think adding $(omegacdot 3)$ $(omegacdot 3)$ times is $omega^2cdot 9$.



This is not true, however, as
$$(omegacdot 3)cdot (omegacdot 3) = omegacdot (3cdotomega)cdot 3 = omega^2cdot 3.$$
The core part of the evaluation is $3cdotomega=omega$ that can be proven in the way of proving $3+omega =omega$ (and the linked question in your comment.)



We would think evaluating $(omegacdot 3+4)cdot(omegacdot 3)$ is not too different from that of $(omegacdot 3)cdot (omegacdot 3)$. The problem is, we have extra $+4$ and we cannot apply the distribution law in the case.
However, the addition in the middle of the expression would disappear when adding $(omegacdot 3+4)$ many times, so we can guess the answer is $omega^2cdot 3$.



You can make our discussion concretely by following the steps of the proof you have linked; that is, use the transfinite induction for $betale omegacdot 3$ to prove
$$(omegacdot 3+4)cdotbeta = begin{cases}
omegacdot (3cdotbeta) &text{if $beta$ is a limit ordinal,} \ omegacdot (3cdotbeta) + 4 & text{if $beta$ is a successor ordinal.}end{cases}$$






share|cite|improve this answer





















  • Ahh I see, thank you very much. So would I right in saying then that something like (w⋅2+2)⋅(w⋅3) would = (w^2).3 ?
    – Fraiku
    Nov 25 at 10:25










  • @Fraiku Yes. $!$
    – Hanul Jeon
    Nov 25 at 10:26










  • Sorry, you are being so helpful I hope you don't mind if I ask you another question. Given the lack of distributive law on the right, I am struggling to know where to start to tackle more complex multiplications such as: ((w^2).2)+(w.3+1))5 or ((w^2).2)+(w.3+1))(w.5)
    – Fraiku
    Nov 25 at 10:32












  • @Fraiku The easiest strategy is evaluate $alphacdotbeta$ for small $beta$ and guess the pattern.
    – Hanul Jeon
    Nov 25 at 10:34










  • So ((w^2).2)+(w.3+1))2 = ((w^2).2)+(w.3+1)+((w^2).2)+(w.3+1) = ((w^2).2)+((w^2).2)+(w.3+1) = ((w^2).4)+w.3+1?
    – Fraiku
    Nov 25 at 10:40











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1 Answer
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You have evaluated $(omegacdot 3+4)cdot 3$ correctly. However, $(omegacdot 3+4)cdot(omegacdot 3)$ is not correctly evaluated. I do not know which step of your evaluation is incorrect, but I guess you think adding $(omegacdot 3)$ $(omegacdot 3)$ times is $omega^2cdot 9$.



This is not true, however, as
$$(omegacdot 3)cdot (omegacdot 3) = omegacdot (3cdotomega)cdot 3 = omega^2cdot 3.$$
The core part of the evaluation is $3cdotomega=omega$ that can be proven in the way of proving $3+omega =omega$ (and the linked question in your comment.)



We would think evaluating $(omegacdot 3+4)cdot(omegacdot 3)$ is not too different from that of $(omegacdot 3)cdot (omegacdot 3)$. The problem is, we have extra $+4$ and we cannot apply the distribution law in the case.
However, the addition in the middle of the expression would disappear when adding $(omegacdot 3+4)$ many times, so we can guess the answer is $omega^2cdot 3$.



You can make our discussion concretely by following the steps of the proof you have linked; that is, use the transfinite induction for $betale omegacdot 3$ to prove
$$(omegacdot 3+4)cdotbeta = begin{cases}
omegacdot (3cdotbeta) &text{if $beta$ is a limit ordinal,} \ omegacdot (3cdotbeta) + 4 & text{if $beta$ is a successor ordinal.}end{cases}$$






share|cite|improve this answer





















  • Ahh I see, thank you very much. So would I right in saying then that something like (w⋅2+2)⋅(w⋅3) would = (w^2).3 ?
    – Fraiku
    Nov 25 at 10:25










  • @Fraiku Yes. $!$
    – Hanul Jeon
    Nov 25 at 10:26










  • Sorry, you are being so helpful I hope you don't mind if I ask you another question. Given the lack of distributive law on the right, I am struggling to know where to start to tackle more complex multiplications such as: ((w^2).2)+(w.3+1))5 or ((w^2).2)+(w.3+1))(w.5)
    – Fraiku
    Nov 25 at 10:32












  • @Fraiku The easiest strategy is evaluate $alphacdotbeta$ for small $beta$ and guess the pattern.
    – Hanul Jeon
    Nov 25 at 10:34










  • So ((w^2).2)+(w.3+1))2 = ((w^2).2)+(w.3+1)+((w^2).2)+(w.3+1) = ((w^2).2)+((w^2).2)+(w.3+1) = ((w^2).4)+w.3+1?
    – Fraiku
    Nov 25 at 10:40
















0














You have evaluated $(omegacdot 3+4)cdot 3$ correctly. However, $(omegacdot 3+4)cdot(omegacdot 3)$ is not correctly evaluated. I do not know which step of your evaluation is incorrect, but I guess you think adding $(omegacdot 3)$ $(omegacdot 3)$ times is $omega^2cdot 9$.



This is not true, however, as
$$(omegacdot 3)cdot (omegacdot 3) = omegacdot (3cdotomega)cdot 3 = omega^2cdot 3.$$
The core part of the evaluation is $3cdotomega=omega$ that can be proven in the way of proving $3+omega =omega$ (and the linked question in your comment.)



We would think evaluating $(omegacdot 3+4)cdot(omegacdot 3)$ is not too different from that of $(omegacdot 3)cdot (omegacdot 3)$. The problem is, we have extra $+4$ and we cannot apply the distribution law in the case.
However, the addition in the middle of the expression would disappear when adding $(omegacdot 3+4)$ many times, so we can guess the answer is $omega^2cdot 3$.



You can make our discussion concretely by following the steps of the proof you have linked; that is, use the transfinite induction for $betale omegacdot 3$ to prove
$$(omegacdot 3+4)cdotbeta = begin{cases}
omegacdot (3cdotbeta) &text{if $beta$ is a limit ordinal,} \ omegacdot (3cdotbeta) + 4 & text{if $beta$ is a successor ordinal.}end{cases}$$






share|cite|improve this answer





















  • Ahh I see, thank you very much. So would I right in saying then that something like (w⋅2+2)⋅(w⋅3) would = (w^2).3 ?
    – Fraiku
    Nov 25 at 10:25










  • @Fraiku Yes. $!$
    – Hanul Jeon
    Nov 25 at 10:26










  • Sorry, you are being so helpful I hope you don't mind if I ask you another question. Given the lack of distributive law on the right, I am struggling to know where to start to tackle more complex multiplications such as: ((w^2).2)+(w.3+1))5 or ((w^2).2)+(w.3+1))(w.5)
    – Fraiku
    Nov 25 at 10:32












  • @Fraiku The easiest strategy is evaluate $alphacdotbeta$ for small $beta$ and guess the pattern.
    – Hanul Jeon
    Nov 25 at 10:34










  • So ((w^2).2)+(w.3+1))2 = ((w^2).2)+(w.3+1)+((w^2).2)+(w.3+1) = ((w^2).2)+((w^2).2)+(w.3+1) = ((w^2).4)+w.3+1?
    – Fraiku
    Nov 25 at 10:40














0












0








0






You have evaluated $(omegacdot 3+4)cdot 3$ correctly. However, $(omegacdot 3+4)cdot(omegacdot 3)$ is not correctly evaluated. I do not know which step of your evaluation is incorrect, but I guess you think adding $(omegacdot 3)$ $(omegacdot 3)$ times is $omega^2cdot 9$.



This is not true, however, as
$$(omegacdot 3)cdot (omegacdot 3) = omegacdot (3cdotomega)cdot 3 = omega^2cdot 3.$$
The core part of the evaluation is $3cdotomega=omega$ that can be proven in the way of proving $3+omega =omega$ (and the linked question in your comment.)



We would think evaluating $(omegacdot 3+4)cdot(omegacdot 3)$ is not too different from that of $(omegacdot 3)cdot (omegacdot 3)$. The problem is, we have extra $+4$ and we cannot apply the distribution law in the case.
However, the addition in the middle of the expression would disappear when adding $(omegacdot 3+4)$ many times, so we can guess the answer is $omega^2cdot 3$.



You can make our discussion concretely by following the steps of the proof you have linked; that is, use the transfinite induction for $betale omegacdot 3$ to prove
$$(omegacdot 3+4)cdotbeta = begin{cases}
omegacdot (3cdotbeta) &text{if $beta$ is a limit ordinal,} \ omegacdot (3cdotbeta) + 4 & text{if $beta$ is a successor ordinal.}end{cases}$$






share|cite|improve this answer












You have evaluated $(omegacdot 3+4)cdot 3$ correctly. However, $(omegacdot 3+4)cdot(omegacdot 3)$ is not correctly evaluated. I do not know which step of your evaluation is incorrect, but I guess you think adding $(omegacdot 3)$ $(omegacdot 3)$ times is $omega^2cdot 9$.



This is not true, however, as
$$(omegacdot 3)cdot (omegacdot 3) = omegacdot (3cdotomega)cdot 3 = omega^2cdot 3.$$
The core part of the evaluation is $3cdotomega=omega$ that can be proven in the way of proving $3+omega =omega$ (and the linked question in your comment.)



We would think evaluating $(omegacdot 3+4)cdot(omegacdot 3)$ is not too different from that of $(omegacdot 3)cdot (omegacdot 3)$. The problem is, we have extra $+4$ and we cannot apply the distribution law in the case.
However, the addition in the middle of the expression would disappear when adding $(omegacdot 3+4)$ many times, so we can guess the answer is $omega^2cdot 3$.



You can make our discussion concretely by following the steps of the proof you have linked; that is, use the transfinite induction for $betale omegacdot 3$ to prove
$$(omegacdot 3+4)cdotbeta = begin{cases}
omegacdot (3cdotbeta) &text{if $beta$ is a limit ordinal,} \ omegacdot (3cdotbeta) + 4 & text{if $beta$ is a successor ordinal.}end{cases}$$







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered Nov 25 at 9:51









Hanul Jeon

17.4k42680




17.4k42680












  • Ahh I see, thank you very much. So would I right in saying then that something like (w⋅2+2)⋅(w⋅3) would = (w^2).3 ?
    – Fraiku
    Nov 25 at 10:25










  • @Fraiku Yes. $!$
    – Hanul Jeon
    Nov 25 at 10:26










  • Sorry, you are being so helpful I hope you don't mind if I ask you another question. Given the lack of distributive law on the right, I am struggling to know where to start to tackle more complex multiplications such as: ((w^2).2)+(w.3+1))5 or ((w^2).2)+(w.3+1))(w.5)
    – Fraiku
    Nov 25 at 10:32












  • @Fraiku The easiest strategy is evaluate $alphacdotbeta$ for small $beta$ and guess the pattern.
    – Hanul Jeon
    Nov 25 at 10:34










  • So ((w^2).2)+(w.3+1))2 = ((w^2).2)+(w.3+1)+((w^2).2)+(w.3+1) = ((w^2).2)+((w^2).2)+(w.3+1) = ((w^2).4)+w.3+1?
    – Fraiku
    Nov 25 at 10:40


















  • Ahh I see, thank you very much. So would I right in saying then that something like (w⋅2+2)⋅(w⋅3) would = (w^2).3 ?
    – Fraiku
    Nov 25 at 10:25










  • @Fraiku Yes. $!$
    – Hanul Jeon
    Nov 25 at 10:26










  • Sorry, you are being so helpful I hope you don't mind if I ask you another question. Given the lack of distributive law on the right, I am struggling to know where to start to tackle more complex multiplications such as: ((w^2).2)+(w.3+1))5 or ((w^2).2)+(w.3+1))(w.5)
    – Fraiku
    Nov 25 at 10:32












  • @Fraiku The easiest strategy is evaluate $alphacdotbeta$ for small $beta$ and guess the pattern.
    – Hanul Jeon
    Nov 25 at 10:34










  • So ((w^2).2)+(w.3+1))2 = ((w^2).2)+(w.3+1)+((w^2).2)+(w.3+1) = ((w^2).2)+((w^2).2)+(w.3+1) = ((w^2).4)+w.3+1?
    – Fraiku
    Nov 25 at 10:40
















Ahh I see, thank you very much. So would I right in saying then that something like (w⋅2+2)⋅(w⋅3) would = (w^2).3 ?
– Fraiku
Nov 25 at 10:25




Ahh I see, thank you very much. So would I right in saying then that something like (w⋅2+2)⋅(w⋅3) would = (w^2).3 ?
– Fraiku
Nov 25 at 10:25












@Fraiku Yes. $!$
– Hanul Jeon
Nov 25 at 10:26




@Fraiku Yes. $!$
– Hanul Jeon
Nov 25 at 10:26












Sorry, you are being so helpful I hope you don't mind if I ask you another question. Given the lack of distributive law on the right, I am struggling to know where to start to tackle more complex multiplications such as: ((w^2).2)+(w.3+1))5 or ((w^2).2)+(w.3+1))(w.5)
– Fraiku
Nov 25 at 10:32






Sorry, you are being so helpful I hope you don't mind if I ask you another question. Given the lack of distributive law on the right, I am struggling to know where to start to tackle more complex multiplications such as: ((w^2).2)+(w.3+1))5 or ((w^2).2)+(w.3+1))(w.5)
– Fraiku
Nov 25 at 10:32














@Fraiku The easiest strategy is evaluate $alphacdotbeta$ for small $beta$ and guess the pattern.
– Hanul Jeon
Nov 25 at 10:34




@Fraiku The easiest strategy is evaluate $alphacdotbeta$ for small $beta$ and guess the pattern.
– Hanul Jeon
Nov 25 at 10:34












So ((w^2).2)+(w.3+1))2 = ((w^2).2)+(w.3+1)+((w^2).2)+(w.3+1) = ((w^2).2)+((w^2).2)+(w.3+1) = ((w^2).4)+w.3+1?
– Fraiku
Nov 25 at 10:40




So ((w^2).2)+(w.3+1))2 = ((w^2).2)+(w.3+1)+((w^2).2)+(w.3+1) = ((w^2).2)+((w^2).2)+(w.3+1) = ((w^2).4)+w.3+1?
– Fraiku
Nov 25 at 10:40


















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