Can the electrostatic force be infinite in magnitude? [closed]2019 Community Moderator Election Unicorn Meta Zoo #1: Why another podcast? Announcing the arrival of Valued Associate #679: Cesar Manara 2019 Moderator Election Q&A - QuestionnaireWhy can you make two repelling positively charged rods touch? Shouldn't the Coulomb force become infinite?Electrostatic and gravitational forces?Does magnitude of a charge influence magnitude of force that individual charge exerts on another chargeLower limit value of electric forceWhat is the “truth” of the electrostatic force?Similarity in the formula of gravitational force and electrostatic forceForce required to break electrostatic bonds between granular matterHow can moving electrons participate in electrostatic interaction?How can the electrostatic force between parallel plates with constant charge be constant when distance changes?Electrostatic potential of a point charge
What is the ongoing value of the Kanban board to the developers as opposed to management
Where did Arya get these scars?
Protagonist's race is hidden - should I reveal it?
Is a self contained air-bullet cartridge feasible?
Will I lose my paid in full property
Processing ADC conversion result: DMA vs Processor Registers
Why isPrototypeOf() returns false?
Getting AggregateResult variables from Execute Anonymous Window
When does Bran Stark remember Jamie pushing him?
Is there a verb for listening stealthily?
What is the purpose of the side handle on a hand ("eggbeater") drill?
Could a cockatrice have parasitic embryos?
How would you suggest I follow up with coworkers about our deadline that's today?
Does every subgroup of an abelian group have to be abelian?
When speaking, how do you change your mind mid-sentence?
What happened to Viserion in Season 7?
What is /etc/mtab in Linux?
What is the term for extremely loose Latin word order?
Is it appropriate to mention a relatable company blog post when you're asked about the company?
My admission is revoked after accepting the admission offer
Bright yellow or light yellow?
Mechanism of the formation of peracetic acid
Putting Ant-Man on house arrest
Has a Nobel Peace laureate ever been accused of war crimes?
Can the electrostatic force be infinite in magnitude? [closed]
2019 Community Moderator Election
Unicorn Meta Zoo #1: Why another podcast?
Announcing the arrival of Valued Associate #679: Cesar Manara
2019 Moderator Election Q&A - QuestionnaireWhy can you make two repelling positively charged rods touch? Shouldn't the Coulomb force become infinite?Electrostatic and gravitational forces?Does magnitude of a charge influence magnitude of force that individual charge exerts on another chargeLower limit value of electric forceWhat is the “truth” of the electrostatic force?Similarity in the formula of gravitational force and electrostatic forceForce required to break electrostatic bonds between granular matterHow can moving electrons participate in electrostatic interaction?How can the electrostatic force between parallel plates with constant charge be constant when distance changes?Electrostatic potential of a point charge
$begingroup$
The magnitude of the electrostatic force between two charges $Q$ and $q$ separated by a distance $r$ is given by $$F=frackqQr^2$$ but the minimum value of $r$ must be $10^-15 rm m$. Therefore, my question is can the electrostatic force ever be infinite?
forces electrostatics electric-fields singularities coulombs-law
$endgroup$
closed as unclear what you're asking by Chair, Aaron Stevens, John Rennie, GiorgioP, Kyle Kanos Mar 26 at 22:04
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
|
show 2 more comments
$begingroup$
The magnitude of the electrostatic force between two charges $Q$ and $q$ separated by a distance $r$ is given by $$F=frackqQr^2$$ but the minimum value of $r$ must be $10^-15 rm m$. Therefore, my question is can the electrostatic force ever be infinite?
forces electrostatics electric-fields singularities coulombs-law
$endgroup$
closed as unclear what you're asking by Chair, Aaron Stevens, John Rennie, GiorgioP, Kyle Kanos Mar 26 at 22:04
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
1
$begingroup$
First, you should explain why you think the minimum value $r$ can be is $10^-15$, since that would help know where you are coming from. Second, if you take this to be true, then wouldn't that necessarily mean the force cannot be infinite? It sounds like you are actually questioning this "minimum $r$" idea, which we cannot comment on since we do not know why you think this is the case.
$endgroup$
– Aaron Stevens
Mar 25 at 14:17
$begingroup$
@AaronStevens I think it's supposed to be the diameter of an electron.
$endgroup$
– Bob D
Mar 25 at 14:26
$begingroup$
@BobD I thought it is supposed to be the length scale of the atomic nucleus?
$endgroup$
– Aaron Stevens
Mar 25 at 14:27
$begingroup$
@AaronStevens Yeah, could be. I my based my comment on the following reference Pauling, Linus. College Chemistry, San Francisco: Freeman, 1964 "The radius of an electron has not been fully determined exactly but it i known to be less than $1^-13$cm. But others have it different. I think the OP
$endgroup$
– Bob D
Mar 25 at 14:35
2
$begingroup$
@AaronStevens I suspect Aditya is referring to the so-called "classical radius of the electron". Aditya - if that's the case, you should edit your question to make this explicit.
$endgroup$
– Emilio Pisanty
Mar 25 at 14:46
|
show 2 more comments
$begingroup$
The magnitude of the electrostatic force between two charges $Q$ and $q$ separated by a distance $r$ is given by $$F=frackqQr^2$$ but the minimum value of $r$ must be $10^-15 rm m$. Therefore, my question is can the electrostatic force ever be infinite?
forces electrostatics electric-fields singularities coulombs-law
$endgroup$
The magnitude of the electrostatic force between two charges $Q$ and $q$ separated by a distance $r$ is given by $$F=frackqQr^2$$ but the minimum value of $r$ must be $10^-15 rm m$. Therefore, my question is can the electrostatic force ever be infinite?
forces electrostatics electric-fields singularities coulombs-law
forces electrostatics electric-fields singularities coulombs-law
edited Mar 25 at 17:32
Qmechanic♦
108k122001253
108k122001253
asked Mar 25 at 14:10
AdityaAditya
173
173
closed as unclear what you're asking by Chair, Aaron Stevens, John Rennie, GiorgioP, Kyle Kanos Mar 26 at 22:04
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
closed as unclear what you're asking by Chair, Aaron Stevens, John Rennie, GiorgioP, Kyle Kanos Mar 26 at 22:04
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
1
$begingroup$
First, you should explain why you think the minimum value $r$ can be is $10^-15$, since that would help know where you are coming from. Second, if you take this to be true, then wouldn't that necessarily mean the force cannot be infinite? It sounds like you are actually questioning this "minimum $r$" idea, which we cannot comment on since we do not know why you think this is the case.
$endgroup$
– Aaron Stevens
Mar 25 at 14:17
$begingroup$
@AaronStevens I think it's supposed to be the diameter of an electron.
$endgroup$
– Bob D
Mar 25 at 14:26
$begingroup$
@BobD I thought it is supposed to be the length scale of the atomic nucleus?
$endgroup$
– Aaron Stevens
Mar 25 at 14:27
$begingroup$
@AaronStevens Yeah, could be. I my based my comment on the following reference Pauling, Linus. College Chemistry, San Francisco: Freeman, 1964 "The radius of an electron has not been fully determined exactly but it i known to be less than $1^-13$cm. But others have it different. I think the OP
$endgroup$
– Bob D
Mar 25 at 14:35
2
$begingroup$
@AaronStevens I suspect Aditya is referring to the so-called "classical radius of the electron". Aditya - if that's the case, you should edit your question to make this explicit.
$endgroup$
– Emilio Pisanty
Mar 25 at 14:46
|
show 2 more comments
1
$begingroup$
First, you should explain why you think the minimum value $r$ can be is $10^-15$, since that would help know where you are coming from. Second, if you take this to be true, then wouldn't that necessarily mean the force cannot be infinite? It sounds like you are actually questioning this "minimum $r$" idea, which we cannot comment on since we do not know why you think this is the case.
$endgroup$
– Aaron Stevens
Mar 25 at 14:17
$begingroup$
@AaronStevens I think it's supposed to be the diameter of an electron.
$endgroup$
– Bob D
Mar 25 at 14:26
$begingroup$
@BobD I thought it is supposed to be the length scale of the atomic nucleus?
$endgroup$
– Aaron Stevens
Mar 25 at 14:27
$begingroup$
@AaronStevens Yeah, could be. I my based my comment on the following reference Pauling, Linus. College Chemistry, San Francisco: Freeman, 1964 "The radius of an electron has not been fully determined exactly but it i known to be less than $1^-13$cm. But others have it different. I think the OP
$endgroup$
– Bob D
Mar 25 at 14:35
2
$begingroup$
@AaronStevens I suspect Aditya is referring to the so-called "classical radius of the electron". Aditya - if that's the case, you should edit your question to make this explicit.
$endgroup$
– Emilio Pisanty
Mar 25 at 14:46
1
1
$begingroup$
First, you should explain why you think the minimum value $r$ can be is $10^-15$, since that would help know where you are coming from. Second, if you take this to be true, then wouldn't that necessarily mean the force cannot be infinite? It sounds like you are actually questioning this "minimum $r$" idea, which we cannot comment on since we do not know why you think this is the case.
$endgroup$
– Aaron Stevens
Mar 25 at 14:17
$begingroup$
First, you should explain why you think the minimum value $r$ can be is $10^-15$, since that would help know where you are coming from. Second, if you take this to be true, then wouldn't that necessarily mean the force cannot be infinite? It sounds like you are actually questioning this "minimum $r$" idea, which we cannot comment on since we do not know why you think this is the case.
$endgroup$
– Aaron Stevens
Mar 25 at 14:17
$begingroup$
@AaronStevens I think it's supposed to be the diameter of an electron.
$endgroup$
– Bob D
Mar 25 at 14:26
$begingroup$
@AaronStevens I think it's supposed to be the diameter of an electron.
$endgroup$
– Bob D
Mar 25 at 14:26
$begingroup$
@BobD I thought it is supposed to be the length scale of the atomic nucleus?
$endgroup$
– Aaron Stevens
Mar 25 at 14:27
$begingroup$
@BobD I thought it is supposed to be the length scale of the atomic nucleus?
$endgroup$
– Aaron Stevens
Mar 25 at 14:27
$begingroup$
@AaronStevens Yeah, could be. I my based my comment on the following reference Pauling, Linus. College Chemistry, San Francisco: Freeman, 1964 "The radius of an electron has not been fully determined exactly but it i known to be less than $1^-13$cm. But others have it different. I think the OP
$endgroup$
– Bob D
Mar 25 at 14:35
$begingroup$
@AaronStevens Yeah, could be. I my based my comment on the following reference Pauling, Linus. College Chemistry, San Francisco: Freeman, 1964 "The radius of an electron has not been fully determined exactly but it i known to be less than $1^-13$cm. But others have it different. I think the OP
$endgroup$
– Bob D
Mar 25 at 14:35
2
2
$begingroup$
@AaronStevens I suspect Aditya is referring to the so-called "classical radius of the electron". Aditya - if that's the case, you should edit your question to make this explicit.
$endgroup$
– Emilio Pisanty
Mar 25 at 14:46
$begingroup$
@AaronStevens I suspect Aditya is referring to the so-called "classical radius of the electron". Aditya - if that's the case, you should edit your question to make this explicit.
$endgroup$
– Emilio Pisanty
Mar 25 at 14:46
|
show 2 more comments
3 Answers
3
active
oldest
votes
$begingroup$
This
but the minimum value of $r$ must be $10^-15 rm m$
sounds like you found a reference to the so-called "classical radius of the electron", possibly with some figures for the radii of atomic nuclei, but you did not fully understand what the former means.
The 'classical radius of the electron' $r_mathrmcl$ is the radius at which a spherical lump of charge would have an electrostatic self-energy equal to the rest energy $E_mathrmrest = m_e c^2$ of the electron. But the key word there is "would": the electron isn't a spherical lump of charge: as far as we can tell, it is a point particle with no internal structure that we've been able to detect ─ with a current experimental precision of the order of $10^-18:rm m$.
It is true, on the other hand, that when you're considering the electrostatic interactions between point particles at length scales shorter than about $10^-10:rm m$ (give or take, depending on what you're doing) you're going to need to change your framework from a classical viewpoint to one based on quantum mechanics, in which electrostatics remains mostly unchanged, but the whole mechanics itself (including the meanings of concepts like "trajectory", "distance" or "force") changes. Once you make that leap, the question of whether the electrostatic force can have infinite values becomes pretty much moot - but the singularity remains.
$endgroup$
$begingroup$
what about Friedrich Bopp's theory of self energy of an electron as discussed in Feyman lectures Vol 2 ? Not applicable here.
$endgroup$
– gansub
Mar 26 at 8:30
add a comment |
$begingroup$
The classical physics equation $F = frackqQr^2$ has to be interpreted using quantum mechanics for sufficiently small length scales. So, its probably not appropriate to say that the force becomes infinite. A typical rule of thumb for the smallest length scale for which this applies is the Compton wavelength $lambda = frachmc$. Here $h$ is Plank's constant, $c$ the speed of light and $m$ the particle mass. For an electron, this comes out to $2.4times 10^-12$m, but for a proton, it would be smaller.
$endgroup$
add a comment |
$begingroup$
Physically, an infinite force is not possible. The fact that the simple electrostatic model (Coulomb's law)
$F=frackqQr^2$
suggests an infinite (or at least an unbounded) force between two point charges as they get closer and closer together tells us that this must be an approximate model which does not hold for very small $r$. Either point charges do not occur in nature, or the $r^-2$ model is replaced by something else for small enough $r$.
$endgroup$
add a comment |
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
This
but the minimum value of $r$ must be $10^-15 rm m$
sounds like you found a reference to the so-called "classical radius of the electron", possibly with some figures for the radii of atomic nuclei, but you did not fully understand what the former means.
The 'classical radius of the electron' $r_mathrmcl$ is the radius at which a spherical lump of charge would have an electrostatic self-energy equal to the rest energy $E_mathrmrest = m_e c^2$ of the electron. But the key word there is "would": the electron isn't a spherical lump of charge: as far as we can tell, it is a point particle with no internal structure that we've been able to detect ─ with a current experimental precision of the order of $10^-18:rm m$.
It is true, on the other hand, that when you're considering the electrostatic interactions between point particles at length scales shorter than about $10^-10:rm m$ (give or take, depending on what you're doing) you're going to need to change your framework from a classical viewpoint to one based on quantum mechanics, in which electrostatics remains mostly unchanged, but the whole mechanics itself (including the meanings of concepts like "trajectory", "distance" or "force") changes. Once you make that leap, the question of whether the electrostatic force can have infinite values becomes pretty much moot - but the singularity remains.
$endgroup$
$begingroup$
what about Friedrich Bopp's theory of self energy of an electron as discussed in Feyman lectures Vol 2 ? Not applicable here.
$endgroup$
– gansub
Mar 26 at 8:30
add a comment |
$begingroup$
This
but the minimum value of $r$ must be $10^-15 rm m$
sounds like you found a reference to the so-called "classical radius of the electron", possibly with some figures for the radii of atomic nuclei, but you did not fully understand what the former means.
The 'classical radius of the electron' $r_mathrmcl$ is the radius at which a spherical lump of charge would have an electrostatic self-energy equal to the rest energy $E_mathrmrest = m_e c^2$ of the electron. But the key word there is "would": the electron isn't a spherical lump of charge: as far as we can tell, it is a point particle with no internal structure that we've been able to detect ─ with a current experimental precision of the order of $10^-18:rm m$.
It is true, on the other hand, that when you're considering the electrostatic interactions between point particles at length scales shorter than about $10^-10:rm m$ (give or take, depending on what you're doing) you're going to need to change your framework from a classical viewpoint to one based on quantum mechanics, in which electrostatics remains mostly unchanged, but the whole mechanics itself (including the meanings of concepts like "trajectory", "distance" or "force") changes. Once you make that leap, the question of whether the electrostatic force can have infinite values becomes pretty much moot - but the singularity remains.
$endgroup$
$begingroup$
what about Friedrich Bopp's theory of self energy of an electron as discussed in Feyman lectures Vol 2 ? Not applicable here.
$endgroup$
– gansub
Mar 26 at 8:30
add a comment |
$begingroup$
This
but the minimum value of $r$ must be $10^-15 rm m$
sounds like you found a reference to the so-called "classical radius of the electron", possibly with some figures for the radii of atomic nuclei, but you did not fully understand what the former means.
The 'classical radius of the electron' $r_mathrmcl$ is the radius at which a spherical lump of charge would have an electrostatic self-energy equal to the rest energy $E_mathrmrest = m_e c^2$ of the electron. But the key word there is "would": the electron isn't a spherical lump of charge: as far as we can tell, it is a point particle with no internal structure that we've been able to detect ─ with a current experimental precision of the order of $10^-18:rm m$.
It is true, on the other hand, that when you're considering the electrostatic interactions between point particles at length scales shorter than about $10^-10:rm m$ (give or take, depending on what you're doing) you're going to need to change your framework from a classical viewpoint to one based on quantum mechanics, in which electrostatics remains mostly unchanged, but the whole mechanics itself (including the meanings of concepts like "trajectory", "distance" or "force") changes. Once you make that leap, the question of whether the electrostatic force can have infinite values becomes pretty much moot - but the singularity remains.
$endgroup$
This
but the minimum value of $r$ must be $10^-15 rm m$
sounds like you found a reference to the so-called "classical radius of the electron", possibly with some figures for the radii of atomic nuclei, but you did not fully understand what the former means.
The 'classical radius of the electron' $r_mathrmcl$ is the radius at which a spherical lump of charge would have an electrostatic self-energy equal to the rest energy $E_mathrmrest = m_e c^2$ of the electron. But the key word there is "would": the electron isn't a spherical lump of charge: as far as we can tell, it is a point particle with no internal structure that we've been able to detect ─ with a current experimental precision of the order of $10^-18:rm m$.
It is true, on the other hand, that when you're considering the electrostatic interactions between point particles at length scales shorter than about $10^-10:rm m$ (give or take, depending on what you're doing) you're going to need to change your framework from a classical viewpoint to one based on quantum mechanics, in which electrostatics remains mostly unchanged, but the whole mechanics itself (including the meanings of concepts like "trajectory", "distance" or "force") changes. Once you make that leap, the question of whether the electrostatic force can have infinite values becomes pretty much moot - but the singularity remains.
answered Mar 25 at 14:55
Emilio PisantyEmilio Pisanty
87.5k23219443
87.5k23219443
$begingroup$
what about Friedrich Bopp's theory of self energy of an electron as discussed in Feyman lectures Vol 2 ? Not applicable here.
$endgroup$
– gansub
Mar 26 at 8:30
add a comment |
$begingroup$
what about Friedrich Bopp's theory of self energy of an electron as discussed in Feyman lectures Vol 2 ? Not applicable here.
$endgroup$
– gansub
Mar 26 at 8:30
$begingroup$
what about Friedrich Bopp's theory of self energy of an electron as discussed in Feyman lectures Vol 2 ? Not applicable here.
$endgroup$
– gansub
Mar 26 at 8:30
$begingroup$
what about Friedrich Bopp's theory of self energy of an electron as discussed in Feyman lectures Vol 2 ? Not applicable here.
$endgroup$
– gansub
Mar 26 at 8:30
add a comment |
$begingroup$
The classical physics equation $F = frackqQr^2$ has to be interpreted using quantum mechanics for sufficiently small length scales. So, its probably not appropriate to say that the force becomes infinite. A typical rule of thumb for the smallest length scale for which this applies is the Compton wavelength $lambda = frachmc$. Here $h$ is Plank's constant, $c$ the speed of light and $m$ the particle mass. For an electron, this comes out to $2.4times 10^-12$m, but for a proton, it would be smaller.
$endgroup$
add a comment |
$begingroup$
The classical physics equation $F = frackqQr^2$ has to be interpreted using quantum mechanics for sufficiently small length scales. So, its probably not appropriate to say that the force becomes infinite. A typical rule of thumb for the smallest length scale for which this applies is the Compton wavelength $lambda = frachmc$. Here $h$ is Plank's constant, $c$ the speed of light and $m$ the particle mass. For an electron, this comes out to $2.4times 10^-12$m, but for a proton, it would be smaller.
$endgroup$
add a comment |
$begingroup$
The classical physics equation $F = frackqQr^2$ has to be interpreted using quantum mechanics for sufficiently small length scales. So, its probably not appropriate to say that the force becomes infinite. A typical rule of thumb for the smallest length scale for which this applies is the Compton wavelength $lambda = frachmc$. Here $h$ is Plank's constant, $c$ the speed of light and $m$ the particle mass. For an electron, this comes out to $2.4times 10^-12$m, but for a proton, it would be smaller.
$endgroup$
The classical physics equation $F = frackqQr^2$ has to be interpreted using quantum mechanics for sufficiently small length scales. So, its probably not appropriate to say that the force becomes infinite. A typical rule of thumb for the smallest length scale for which this applies is the Compton wavelength $lambda = frachmc$. Here $h$ is Plank's constant, $c$ the speed of light and $m$ the particle mass. For an electron, this comes out to $2.4times 10^-12$m, but for a proton, it would be smaller.
answered Mar 25 at 17:08
Laurence LurioLaurence Lurio
1144
1144
add a comment |
add a comment |
$begingroup$
Physically, an infinite force is not possible. The fact that the simple electrostatic model (Coulomb's law)
$F=frackqQr^2$
suggests an infinite (or at least an unbounded) force between two point charges as they get closer and closer together tells us that this must be an approximate model which does not hold for very small $r$. Either point charges do not occur in nature, or the $r^-2$ model is replaced by something else for small enough $r$.
$endgroup$
add a comment |
$begingroup$
Physically, an infinite force is not possible. The fact that the simple electrostatic model (Coulomb's law)
$F=frackqQr^2$
suggests an infinite (or at least an unbounded) force between two point charges as they get closer and closer together tells us that this must be an approximate model which does not hold for very small $r$. Either point charges do not occur in nature, or the $r^-2$ model is replaced by something else for small enough $r$.
$endgroup$
add a comment |
$begingroup$
Physically, an infinite force is not possible. The fact that the simple electrostatic model (Coulomb's law)
$F=frackqQr^2$
suggests an infinite (or at least an unbounded) force between two point charges as they get closer and closer together tells us that this must be an approximate model which does not hold for very small $r$. Either point charges do not occur in nature, or the $r^-2$ model is replaced by something else for small enough $r$.
$endgroup$
Physically, an infinite force is not possible. The fact that the simple electrostatic model (Coulomb's law)
$F=frackqQr^2$
suggests an infinite (or at least an unbounded) force between two point charges as they get closer and closer together tells us that this must be an approximate model which does not hold for very small $r$. Either point charges do not occur in nature, or the $r^-2$ model is replaced by something else for small enough $r$.
answered Mar 25 at 14:47
gandalf61gandalf61
814210
814210
add a comment |
add a comment |
1
$begingroup$
First, you should explain why you think the minimum value $r$ can be is $10^-15$, since that would help know where you are coming from. Second, if you take this to be true, then wouldn't that necessarily mean the force cannot be infinite? It sounds like you are actually questioning this "minimum $r$" idea, which we cannot comment on since we do not know why you think this is the case.
$endgroup$
– Aaron Stevens
Mar 25 at 14:17
$begingroup$
@AaronStevens I think it's supposed to be the diameter of an electron.
$endgroup$
– Bob D
Mar 25 at 14:26
$begingroup$
@BobD I thought it is supposed to be the length scale of the atomic nucleus?
$endgroup$
– Aaron Stevens
Mar 25 at 14:27
$begingroup$
@AaronStevens Yeah, could be. I my based my comment on the following reference Pauling, Linus. College Chemistry, San Francisco: Freeman, 1964 "The radius of an electron has not been fully determined exactly but it i known to be less than $1^-13$cm. But others have it different. I think the OP
$endgroup$
– Bob D
Mar 25 at 14:35
2
$begingroup$
@AaronStevens I suspect Aditya is referring to the so-called "classical radius of the electron". Aditya - if that's the case, you should edit your question to make this explicit.
$endgroup$
– Emilio Pisanty
Mar 25 at 14:46