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#131
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Gravitational Doppler
Lester Zick wrote: On 21 Aug 2006 06:15:07 -0700, "George Dishman" wrote: Lester Zick wrote: .. If you can't make your own arguments there's nothing much to criticize except technique. OK, if you want me to make my own arguments try this. You first suggested that globular clusters were amongst the youngest objects in the galaxy and later changed to say you were interested in the relative ages. Yeah, George, look I have absolutely no further interest in your misrepresentations of the issue I raised. I've shown you the quote of the issue you raised several times so there is no misrepresentation on my part, but I understand you were never really interested in relative ages of anything, you just wanted to have an argument. You seem interested in pursuing a problem I've long since given up clarifying and doing so in highly prejudicial terms. Not at all, I carefully wrote the last post just to include the factual measurements without criticism of you or your questions. You are the one trying to turn it back into a dispute. The age of the stars in NGC 6397, as determined by means of stellar evolution models, is 13400 +/- 800 million years. Well goodie. That's just swell. Just a simple fact, that is the age the current best measurement gives. The relative ages of the Milky Way and NGC 6397 has been determined by measuring Beryllium content and is found to be about a 200 million year difference making the age of the galaxy 13600 +/- 800, i.e. the galaxy is very slightly older than the cluster. And what about the age of the Milky Way as determined by measuring its Alka Seltzer content? Carry on Lester, I don't need to use "prejudicial terms" when you demonstrate your attitude so effectively yourself. The age of NGC 6397 is therefore 98.5% of the age of the galaxy and since there are other younger structures in the galaxy that makes the cluster "one of the oldest structures in the galaxy". Well the problem here is that even given these particular relative ages that doesn't make globular clusters older than the galaxy .. Why do you think that is a problem? When you asked about the relative ages of the Milky way and clusters, a week ago, I gave you the link to the page that said that relatively the galaxy was 200 million years older. You chose not to read the page and assumed I was disagreeing with you as any troll would. .. and certainly not one of the oldest objects in the universe in any categorical priority sense of oldest objects. I said nothing of the universe above, that comes next. The age of the universe is 13700 million years measured by the WMAP mission. The age of the universe is not an issue in Newtonian mechanics. We've already established that. We have established that indeed. The reason it isn't an issue is that Newtonian mechanics gives a similar age. This is nothing but an ad hoc assertion akin to dark matter which should read "if all our assumptions, assertions, and fantasies regarding CMBR and the Hubble redshift should turn out to be true we might then be able to chronicle the age of the universe otherwise not". More unsubstantiated ranting Lester? If you want to query the age, there are a raft of measurements on which it relies from the calibration of distances using local parallax onwards that you could examine, but I don't think that's your style. The age of NGC 6397 is therefore 97.8% of the age of the universe and since there are other younger structures in the universe that makes the cluster "one of the oldest structures in the universe". And not even in your wildest dreams does it make it categorically older than the galaxy. Right, it categorically makes it younger as I pointed out to you last weekend, and as you would have known if you had bothered to read the page, or maybe you did but clearly all you wanted was an argument so the fact that I had agreed with you was a problem for you. That is the second time I have agreed with you against the posts of others in the group and both times you have simply argued with me for my pains. It's called trolling, Lester, and I'm not interested if that's all you are looking for. None of the above ages relies on the dynamics of cluster structure so your comments on that aspect are not relevant. And none of your assertions makes anything older or younger than anything else in categorical terms. On the contrary, the beryllium measurement categorically makes the galaxy older than the cluster as I pointed out over a week ago. Oh and it's easy to validate my assertion that those are the measured values, just look at the ESO page I cited. George |
#132
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Gravitational Doppler
On 22 Aug 2006 01:20:38 -0700, "George Dishman"
wrote: Yes, yes, George, it's good to see we've finally reached agreement on the fundamental issue I raised initially. I agree that the virial theorem supports my view on the relative age of globular clusters. The problem has always been that those who disagree with my analysis have looked at the problem backward, initially trying to grasp the motions of individual stars within a globular cluster instead of the cluster as a whole. The fact seems to be that globular clusters have no net angular momentum themselves. Consequently we must infer that motions of individual stars within the cluster are completely nugatory and that angular momenta within the cluster cancel each other and centers of gravity for those angular momenta must be stationary with respect to the cluster or the cluster itself would have angular momentum. The result of all this is that globular clusters must be collapsing along the lines of those stationary centers of gravity. This much of course should be intuitively obvious to the casual observer of Newtonian mechanics however difficult it may be to grasp by the average student of astronomy. Perhaps it is the case that average students of astronomy are just average students to begin with and only take astronomy in the first place because they're too lazy or stupid to cope with actual celestial mechanics. In any event in the interests of full discolsure I've enclosed a link to you where if they're interested the halt and lame can further research your views on various aspects of the problem which read more like a couple of turbid chapters from Tolstoy than any kind of effective mechanical analysis of the issues under consideration. Lester Zick ~v~~ |
#133
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Gravitational Doppler
Lester Zick writes: On 21 Aug 2006 03:25:34 -0400, Craig Markwardt wrote: Lester Zick writes: On 19 Aug 2006 14:19:24 -0400, Craig Markwardt wrote: Lester Zick writes: ... snip ... It means I think the sky is falling in gc's just the way it does in every celestial object whose centers of gravity are stationary with respect to one another. ... snip ... What exactly do you mean by, * "centers of gravity", and that they * "stationary with respect to one another" Perfectly reasonable questions. I'm not asking for an "it's obvious" answer, but rather, what exactly you think the terms you used mean in terms of geometry and perhaps mathematics. I take the term "centers of gravity" to mean the centers through which universal gravitational attraction operates. Each star in a globular cluster has its own local internal center of gravity and each star in various cominations with other stars has a non local center of gravity presumably lying somewhere between or among them through which gravitational attraction for the combination acts in relation to centers of gravity for other combinations.And these centers of gravity exist for every possible combination of stars within the cluster. And every possible combination of stationary and moving stars within a cluster has to be reckoned in terms of all centers of gravity among all the combinations and not just exclusively between each pair of stars within the cluster or for the cluster as a whole in calculating net angular momentum for the cluster. Wouldn't it be more straightforward to calculate the cluster angular momentum about a given axis based on a sum of the individual stars' angular momenta?[*] After all, that is the formal definition of angular momentum, isn't it? Regardless of how you add them up the sum is still roughly zero provided you add them all up and not just a few in relation to a specific axis. However, since classical total angular momentum is not defined in the manner which you describe, you would need to substantiate your claim with extensive theoretical work, which you have not done. [*] By that I mean, L_total = Sum[ L_i ] = Sum[ r_i x p_i ], where r_i and p_i are the ith star's distance from the axis and linear momentum, and "x" indicates a vector cross product. And secondly, on what evidence do you claim that "centers of gravity are stationary with respect to one another?" Well this may not appear obvious however in calculating net angular momentum for the cluster as a whole we know two basic things: first the motion of various stars in the cluster individually and second the net angular momentum for the cluster as a whole of approximately zero. Thus we can easily construct an equation where the sum of all angular momenta for all possible combinations of stars in a globular cluster equals zero. So regardless how we take various combinations of angular momenta for various centers of gravity within the cluster we have to recognize that their sum must be zero for the cluster itself to have a net angular mometum approximately zero. Which means in turn that all combinations must offset one another in aggregate. Hence even though some combinational centers may not offset one another directly, all centers of gravity within the cluster have to be roughly stationary with respect to all other centers of gravity regardless of a presence of non zero angular momentum for certain combinations within the cluster. How does your conclusion follow? Because the net angular momentum for the cluster as a whole is roughly zero. Consequently regardless of individual angular momenta considered in isolation the aggregate of all angular momenta must be roughly zero too. Otherwise the cluster itself must have non zero angular momentum. Your original conclusion still does not follow. Even if the total sum angular momentum of an ensemble is zero, one cannot conclude that the individual components of the sum must be zero. Hence one cannot conclude that the individual components are "stationary." First, you've been writing about angular momentum, so what step of logic allows one to translate from the domain of angular momentum to "roughly stationary" points? For example, the total angular momentum of a system can be zero when the total energy or linear momentum is not. I'm not talking about linear momentum here.As far as different domains of angular momentum are concerned we're just adding them up. They have to equal zero whether or not isolated domains have energy or linear momentum. It's quite possible for moving bodies with kinetic energy and linear momentum to possess offsetting angular momenta with respect to various centers of gravity. You claimed that something was "stationary." In classical mechanics if a body is stationary, it is not moving. A body cannot have "kinetic energy and linear momentum" and also be stationary. Second, it is easy to construct a sum of two functions which is zero but whose individual values are not. Sure. The problem is that we have to wind up with centers of gravity stationary with respect to each other or the angular momentum of the object as a whole will have some net angular momentum. For example, consider three identical stars arranged along the X axis at positions (-1 pc), (0 pc), (+1 pc),[*] with the outer two stars moving apart and the center star held fixed (with respective velocities: (-1 pc/yr), (0 pc/yr), (+1 pc/yr)). By any definition, the total linear and angular momentum of this system is zero. And yet, the stars are moving apart. The "centers of gravity" as you define them are also moving apart from each other and thus not "stationary." Thus, your conclusion is not rigorous. Which centers of gravity? That for the stars individually considered in isolation or the center of gravity for the system as a whole? The fact that the stars themselves are moving apart is irrelevant. The center of gravity for the system itself is stationary. The centers of gravity as I define them are only moving apart for the individual stars and not for the system as a whole. You claimed that one must consider *all* possible combinations of "centers of gravity." For the triplet of stars mentioned, there are three possible pairs of stars, three possible 2-1 combinations, and a sum of all three, for a total of seven combinations. All of those "centers of gravity" are moving with respect to each other, even though the total linear and angular momenta are zero. Thus, your claim leads to a contradiction. If you are now changing your claim to only discuss the angular momentum of the center of mass alone, that is a different matter, but it is not what you originally claimed. .... snip ... Of course I maintain that given such an analysis with effectively stationary centers of gravity overall we're faced with a de facto necessity for collapse along lines of stationary centers of gravity. It's what I call the Chicken Little Hypothesis. In other words the sky is falling. How does that follow either? Even if, for the sake of argument, the "centers of gravity" were "stationary," you have defined them as imaginary points. It's not a question of how I've defined them.They're defined by Newton as much as anyone as the centers through which universal gravitational attraction works. And they're no more imaginary than the local centers of attraction through which gravitational attraction works inside stars. Just because you can't associate any material element with them outside a star doesn't mean they don't actually exist. That is not relevant. "Centers of gravity" are still imaginary points. Therefore, they are not attracted to each other by gravity, nor do they have angular momentum or energy. They do not necessarily "collapse" by themselves. As you defined them, they merely exist as points defined by the various stars in the cluster. Thus your conclusion does not follow. The relevant question is regards the motions of the individual stars. Then any follow-on discussion of "centers of gravity" can be computed immmediately. .... snip ... Let's try a simple example. Suppose we have a globular cluster with roughly zero net angular momentum. And let's suppose through the magic of TV we can define opposing centers of gravity in respective hemispheres A and B around which all stars in those hemispheres have roughly equal and opposite aggregate angular momentum. The question then is can A and B be moving with respect to each other? Obviously not. They have to be stationary with respect to one another. Your example is not well enough defined. If your "A" and "B" are defined in terms of a fixed set of stars, initially in two hemispheres; then of course, as the stars move, the centers of mass of the two sets of stars will move in some complicated pattern. If your "A" and "B" are always defined in terms of the two fixed hemispheres, then of course the hemispheres will not move since you have defined them to be fixed. Stars will pass between the boundaries of the two hemispheres, thus blurring the concept of "center of gravity." Thus, your example is not sufficient. ....snip... CM |
#134
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Gravitational Doppler
Lester Zick wrote: On 22 Aug 2006 01:20:38 -0700, "George Dishman" wrote: my entire post snipped by Lester Yes, yes, George, it's good to see we've finally reached agreement on the fundamental issue I raised initially. Nice to see we have cleared up that clusters are some of the oldest objects in the galaxy. I agree that the virial theorem supports my view on the relative age of globular clusters. It doesn't, the virial theorem was not relevant to that determination at all. The relative difference in ages was determined by beryllium abundances and has never been in contention. You would have known that if you had read the ESO web page I posted when you first asked that question. We never disagreed on that. In fact it is quite likely that the formation of the galaxy took some time and was probably ongoing when the cluster formed but the ESO measurement confirms what you said on their relative ages. The problem has always been that those who disagree with my analysis have looked at the problem backward, initially trying to grasp the motions of individual stars within a globular cluster instead of the cluster as a whole. The fact seems to be that globular clusters have no net angular momentum themselves. Consequently we must infer that motions of individual stars within the cluster are completely nugatory and that angular momenta within the cluster cancel each other Essentially that is correct, the net is small compared to the sum of the individual stars' momenta though it is not exactly zero. and centers of gravity for those angular momenta must be stationary with respect to the cluster or the cluster itself would have angular momentum. No, the angular momenta of individual stars can be high as long as they cancel as you say above. That is where the virial theorem comes in. For a globular cluster, it gives: KE = -1/2 PE or the average kinetic energy for individual stars is half of their average negative gravitational potential energy. Since the directions of the individual stars motions are randomised by the gravitational interactions, they are also random and that gives a random distribution of angular momenta about the cluster's centre of momentum even though the total is near to zero. The result of all this is that globular clusters must be collapsing along the lines of those stationary centers of gravity. Nope, it says the opposite. Since the individual stars have a distribution of angular momenta, it is thefore a result of Newtonian mechanics that the stars do not all rush directly to the centre. The distribution of kinetic energies also includes a tail so there will be a few stars whose kinetic energy is greater than is required for escape so the cluster "evaporates" over long time scales. Since the highest velocity stars also have the highest momentum, that doesn't alter the conclusion that the cluster won't collapse to a disc. They do undergo core collapse of course but that's not what you are describing. more childish attempts at insults snipped. George |
#135
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Gravitational Doppler
On 23 Aug 2006 01:04:20 -0700, "George Dishman"
wrote: Lester Zick wrote: On 22 Aug 2006 01:20:38 -0700, "George Dishman" wrote: Well, George, I didn't snip your entire post as you claim; I just didn't see anything worth saving. I imagine it's still out there lost in cyberspace which is pretty much just where it belongs. It's true that the virial theorem support my interpretation of globular cluster collapse and I'm glad to know you concur that globular clusters are some of the youngest objects in the universe. As for your analysis of the exchange of PE and KE in inverse square conic section orbits. It's totally irrelevant and about as original as the rest of your many and varied misconceptions being hoary with age since the days of Kepler and Newton. But keep plodding along. It's what the British do. Lester Zick ~v~~ |
#136
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Gravitational Doppler
"Lester Zick" wrote in message ... On 23 Aug 2006 01:04:20 -0700, "George Dishman" wrote: Lester Zick wrote: On 22 Aug 2006 01:20:38 -0700, "George Dishman" wrote: Well, George, I didn't snip your entire post as you claim; I just didn't see anything worth saving. Of course you didn't Lester, but then what you see is seldom what I write. ... It's true that the virial theorem support my interpretation of globular cluster collapse and I'm glad to know you concur that globular clusters are some of the youngest objects in the universe. ROFL, so you have been reduced to telling a pack of lies Lester. That's not what your supposed to achieve if you are going to become an effective troll. plonk |
#137
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Gravitational Doppler
On Wed, 23 Aug 2006 20:18:41 +0100, "George Dishman"
wrote: There's nothing much to what you write, George. It's out there if anyone wants to look. You complain that I tell lie after lie whereas you just tell the same lie over and over. And if I ever want to become a troll I'll be sure to ask your help. Lester Zick ~v~~ |
#138
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Gravitational Doppler
On 22 Aug 2006 14:43:22 -0400, Craig Markwardt
wrote: Lester Zick writes: On 21 Aug 2006 03:25:34 -0400, Craig Markwardt wrote: Lester Zick writes: On 19 Aug 2006 14:19:24 -0400, Craig Markwardt wrote: Lester Zick writes: ... snip ... It means I think the sky is falling in gc's just the way it does in every celestial object whose centers of gravity are stationary with respect to one another. ... snip ... What exactly do you mean by, * "centers of gravity", and that they * "stationary with respect to one another" Perfectly reasonable questions. I'm not asking for an "it's obvious" answer, but rather, what exactly you think the terms you used mean in terms of geometry and perhaps mathematics. I take the term "centers of gravity" to mean the centers through which universal gravitational attraction operates. Each star in a globular cluster has its own local internal center of gravity and each star in various cominations with other stars has a non local center of gravity presumably lying somewhere between or among them through which gravitational attraction for the combination acts in relation to centers of gravity for other combinations.And these centers of gravity exist for every possible combination of stars within the cluster. And every possible combination of stationary and moving stars within a cluster has to be reckoned in terms of all centers of gravity among all the combinations and not just exclusively between each pair of stars within the cluster or for the cluster as a whole in calculating net angular momentum for the cluster. Wouldn't it be more straightforward to calculate the cluster angular momentum about a given axis based on a sum of the individual stars' angular momenta?[*] After all, that is the formal definition of angular momentum, isn't it? Regardless of how you add them up the sum is still roughly zero provided you add them all up and not just a few in relation to a specific axis. However, since classical total angular momentum is not defined in the manner which you describe, you would need to substantiate your claim with extensive theoretical work, which you have not done. What do you mean classical angular momentum is not defined in the manner I describe? I don't define angular momentum at all classical or otherwise. Classical angular momentum is defined as the vector cross product L=r x p. Do you actually mean to tell me that you really don't understand how to resolve and add vectors in three dimensions without extensive theoretical work on my part? [*] By that I mean, L_total = Sum[ L_i ] = Sum[ r_i x p_i ], where r_i and p_i are the ith star's distance from the axis and linear momentum, and "x" indicates a vector cross product. And secondly, on what evidence do you claim that "centers of gravity are stationary with respect to one another?" Well this may not appear obvious however in calculating net angular momentum for the cluster as a whole we know two basic things: first the motion of various stars in the cluster individually and second the net angular momentum for the cluster as a whole of approximately zero. Thus we can easily construct an equation where the sum of all angular momenta for all possible combinations of stars in a globular cluster equals zero. So regardless how we take various combinations of angular momenta for various centers of gravity within the cluster we have to recognize that their sum must be zero for the cluster itself to have a net angular mometum approximately zero. Which means in turn that all combinations must offset one another in aggregate. Hence even though some combinational centers may not offset one another directly, all centers of gravity within the cluster have to be roughly stationary with respect to all other centers of gravity regardless of a presence of non zero angular momentum for certain combinations within the cluster. How does your conclusion follow? Because the net angular momentum for the cluster as a whole is roughly zero. Consequently regardless of individual angular momenta considered in isolation the aggregate of all angular momenta must be roughly zero too. Otherwise the cluster itself must have non zero angular momentum. Your original conclusion still does not follow. Even if the total sum angular momentum of an ensemble is zero, one cannot conclude that the individual components of the sum must be zero. Hence one cannot conclude that the individual components are "stationary." I didn't say the individual components of the sum must be zero. I said they have to aggregate to zero.That means that various angular momenta taken in whatever combinations have to offset each other. And if the individual components of all combinations are not roughly stationary with respect to one another the sum of angular momenta for the cluster as a whole will certainly not be roughly zero. First, you've been writing about angular momentum, so what step of logic allows one to translate from the domain of angular momentum to "roughly stationary" points? For example, the total angular momentum of a system can be zero when the total energy or linear momentum is not. I'm not talking about linear momentum here.As far as different domains of angular momentum are concerned we're just adding them up. They have to equal zero whether or not isolated domains have energy or linear momentum. It's quite possible for moving bodies with kinetic energy and linear momentum to possess offsetting angular momenta with respect to various centers of gravity. You claimed that something was "stationary." In classical mechanics if a body is stationary, it is not moving. A body cannot have "kinetic energy and linear momentum" and also be stationary. Why not? We're discussing angular momentum here not linear momentum and kinetic energy. Two bodies of equal mass in opposing orbits have zero net angular momentum because their vector cross products L=r x p offset one another and yet they still have net kinetic energy in gross linear terms because kinetic energy is not a vector. Second, it is easy to construct a sum of two functions which is zero but whose individual values are not. Sure. The problem is that we have to wind up with centers of gravity stationary with respect to each other or the angular momentum of the object as a whole will have some net angular momentum. For example, consider three identical stars arranged along the X axis at positions (-1 pc), (0 pc), (+1 pc),[*] with the outer two stars moving apart and the center star held fixed (with respective velocities: (-1 pc/yr), (0 pc/yr), (+1 pc/yr)). By any definition, the total linear and angular momentum of this system is zero. And yet, the stars are moving apart. The "centers of gravity" as you define them are also moving apart from each other and thus not "stationary." Thus, your conclusion is not rigorous. Which centers of gravity? That for the stars individually considered in isolation or the center of gravity for the system as a whole? The fact that the stars themselves are moving apart is irrelevant. The center of gravity for the system itself is stationary. The centers of gravity as I define them are only moving apart for the individual stars and not for the system as a whole. You claimed that one must consider *all* possible combinations of "centers of gravity." For the triplet of stars mentioned, there are three possible pairs of stars, three possible 2-1 combinations, and a sum of all three, for a total of seven combinations. All of those "centers of gravity" are moving with respect to each other, even though the total linear and angular momenta are zero. Thus, your claim leads to a contradiction. So how is it the vector sum of all those angular momenta around all those centers of gravity add up to zero? If you are now changing your claim to only discuss the angular momentum of the center of mass alone, that is a different matter, but it is not what you originally claimed. And it's not what I mean. It doesn't really matter whether the vector sum of all angular momenta is taken with respect to the center of the mass alone. The fact is their vector sum is roughly zero. ... snip ... Of course I maintain that given such an analysis with effectively stationary centers of gravity overall we're faced with a de facto necessity for collapse along lines of stationary centers of gravity. It's what I call the Chicken Little Hypothesis. In other words the sky is falling. How does that follow either? Even if, for the sake of argument, the "centers of gravity" were "stationary," you have defined them as imaginary points. It's not a question of how I've defined them.They're defined by Newton as much as anyone as the centers through which universal gravitational attraction works. And they're no more imaginary than the local centers of attraction through which gravitational attraction works inside stars. Just because you can't associate any material element with them outside a star doesn't mean they don't actually exist. That is not relevant. "Centers of gravity" are still imaginary points. Therefore, they are not attracted to each other by gravity, nor do they have angular momentum or energy. They do not necessarily "collapse" by themselves. As you defined them, they merely exist as points defined by the various stars in the cluster. Thus your conclusion does not follow. The relevant question is regards the motions of the individual stars. Then any follow-on discussion of "centers of gravity" can be computed immmediately. As Newton defined them centers of gravity are merely points through which gravitation acts. The center of gravity for a star is no more or less real than the center of gravity between stars. ... snip ... Let's try a simple example. Suppose we have a globular cluster with roughly zero net angular momentum. And let's suppose through the magic of TV we can define opposing centers of gravity in respective hemispheres A and B around which all stars in those hemispheres have roughly equal and opposite aggregate angular momentum. The question then is can A and B be moving with respect to each other? Obviously not. They have to be stationary with respect to one another. Your example is not well enough defined. If your "A" and "B" are defined in terms of a fixed set of stars, initially in two hemispheres; then of course, as the stars move, the centers of mass of the two sets of stars will move in some complicated pattern. If your "A" and "B" are always defined in terms of the two fixed hemispheres, then of course the hemispheres will not move since you have defined them to be fixed. I haven't "defined" them to be any such thing. I've said either they are fixed in relation to one another or the cluster as a whole must have non zero angular momentum. Stars will pass between the boundaries of the two hemispheres, thus blurring the concept of "center of gravity." Thus, your example is not sufficient. Yeah, look, Craig, I don't know where you get your ideas on vector arithmetic and blurred centers of gravity. You seem sincere yet these are or should be basic mechanical concepts in first year collegiate math. And what I'm seeing so far is a pretty gross deficiency on the part of almost everyone in sci.astro in basic vector mechanics. And I'm really beginning to regret having broached the topic at all. It's such a simple proposition that I couldn't begin to conceive of all the ridiculous mental constipation and rationalization it's generated. Lester Zick ~v~~ |
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