Reviews Written By: AN8L1MSBP7I67provided by Amazon.com |
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 | Sonicare Elite 7300 Power Toothbrush ( e7300 ) | |
 | "works but so does the cheaper CVS sonic brush" | 2008-03-10 |
| Manual brushing can't achieve so many strokes/minute like the sonic type brushes. The result is they really work better than manual (just my experimental observation) - teeth are cleaner yet not as clean and smooth as after dental cleaning despite the marketing claims. Don't delude yourself - sonic brushes can't clean between the teeth despite the fantastic marketing claims about the 'ultrasonic technology' lol. You will need flosing, interdental brushes or better water jet for that. Sonic vibrating brushes are gentler on the gums compared to the rotating brushes.
After using the sonicare brush for a month, I've replaced it with the CVS sonic brush which to my opinion cleans better - bigger brush and better contact with teeth. The only 'advantages' of sonicare is that its timer beeps every 30 seconds while the CVS timer just turns off the brush after 2 minutes of brushing (you can start it again to continue brushing) and sonicare has a charge indicator while CVS hasn't. The biggest advantage of CVS is the significantly lower price for the unit, which includes the charger, a UV sanitizer and 3 brush heads. The replacement CVS brush heads are way cheaper than the sonicare ones which appparently are made of gold, otherwise I can't understand why I am expected to pay $25-$35 for two plastic brush heads LOL The thing I don't like about both sonicare and CVS brushes is that they don't use regular rechargable batteries so when their battery dies in a few years you will have to throw away the whole unit and get a new one. | ||
 | Remington MS-5200 Titanium MicroScreen (MS5200DT) | |
| "overpiced, shaves like the cheaper MS2 370" | 2007-11-03 |
| I was hoping this shaver to replace my way cheaper Remington MS2 370 but it didn't. It shaves no worse and no better than MS2 370. You can't get a shave as close as a blade with electric razor, no matter which brand, but it's acceptable. My biggest hope was that the mini-foil will improve shaving under the chin. I am a slim guy and have 'valleys and hills' there that are hard to shave with the big foils. Unfortunately, the mini-foil is simply incapable of cutting the hairs and I continue to shave the area with the trimmer and then the big foils. On top of that, the shaver needs 12 hours for recharging while my MS2 370 charges in an hour and in 5 minutes is charged enough for a shave if you are in a hurry. It is beyond my comprehension why would Remington try to sell a model with a charging system inferior to the twice cheaper model and on top of that it doesn't shave better. What were they thinking in their marketing department ???? | ||
 | The Variational Principles of Mechanics (Dover Books on Physics and Chemistry) | |
 | "a lot of unfamiliar variational tricks, sometimes lacks proofs or underexplains" | 2007-07-18 |
| I've read this gem and done most of the evercises in about 3 months. Before that legendary book I'd had the usual crappy course in Classical Mechanics based on Goldstein. The bottom line is the book will show you a lot of advanced material and unfamiliar manipulations. On the other hand there are sometimes statements lacking proof or more detailed lucid explanation. The book is appropriate for readers that already know what action is, totall beginners will be too shocked by the new concepts and won't be able to pick up the important nuances revealed by Lanczos. Lanczos work clarified some of the concepts in which my CM course failed: - the important difference in treating holonomic and nonholonomic constraints - exact constraints are mathematical idealization of infinitely rigid constraint forces - Lagrange multipliers for functionals (actions) not only functions - the logical thread virtual work -> d'Alembert -> Hamilton's principle - the connection between the action in configuration space and in phase space The book introduced me to topics not covered by the course, which was my initial goal: - elimination of ignorable variables in L or H formulation - canonical transformations, definition and importance - generating function of canonical transformation - test for canonicity of transformation using Poisson brackets - integral invariants of canonical transformations - Hamilton's principal function - Hamilton-Jackobi equation and analogy with optical wave surfaces - separation of variables in H-J equation - action-angle variables for separable periodic systems - evolution of the system as a sequence of canonical transformation - introducing geometry and geodesics in phase space The reading definitely increased my freedom in manipulating the variational problem into equivalent variational problem. Examples of the two most weird for me manipulations are in the appendices. In the first appendix the Hamiltonian formulation is derived from the Lagrangian by introducing new variables, constraints and corresponding Lagrange multipliers, and then eliminating the variables. In appendix II, the most popular cases of Noether's theorem are derived by introducing new field variables in the action - I had no idea that was allowed. Very interesting was the idea that the world line of the system in configuration space can be parametrized with arbitrary parameter and the time becomes a function of that parameter that is varied together with the other generalized coordinates. Such variation is normal for GR but I've never seen it done in non-relativistic mechanics. EDIT: Sept 2008. Recently I've found a textbook that clearly explains some of the fuzzy examples in Lanczos like varying the time: "Analytical Mechanics for Relativity and Quantum Mechanics" by Oliver Johns. Some of the other reviews described the book as 'lucid'. I find that eggagerated - although the book shows lots of unfamiliar manipulations, sometimes proofs of validity or the necessary more detailed conceptual or calculational explanations are lacking. An example is the inclusion, all of a sudden, of the time as variable to be varied - where is the proof one is allowed to do that? In another case, the book tells you that by nullifying the boundary term when varying the action, one gets 'natural' boundary conditions for the Euler-Lagrange diff. equations. I failed to see how the physics of the problem would demand exactly those boundary conditions. Where the analogy between mechanics and optics was discussed, the book creates the impression it derived the Fermat's principle but in reality it simply proved that the path following the gradient of of constant surfaces is shortest between two points. So there is a certain gegree of fuzziness on calculational level (lacking proofs of validity) or conceptual level (underexplained concepts and relations). I liked the the abundance of historical notes. You will learn that there are several formulations of the least action principle - Euler and Lagrange version, Jackobi version and Hamilton version. Each subsection has a small summary and there are a few problems per section to illustrate the main ideas but not enough for exercises. There are two chapters that I think appeared in later editions and are too sketchy compared to the book core: Chapter 9 discusses special relativity where you can see that guessing the relativistic Lagrangian on general grounds of Lorentz invariance gives almost effortlessly the relativistic dynamics without the usual gedanken experiments. At the end, Lanczos dives a little into GR using the Schwartzchild metric to derive orbits, bending of light rays and gravitational redshift around spherical body. Chapter 11 gives a short presentation of fluid mechanics (a little unclear derivation, in Lagrange and Euler coordinates), elasticity, and electromagnetism. Noether's principle is used to derive the canonical and the symmetric energy momentum tensor. I haven't seen a crystal clear derivation of Noether anywhere and Lancsoz is not an exception. The problem is as usual ommiting what exactly is being transformed and why is that allowed. | ||
 | An Introduction to the Standard Model of Particle Physics | |
| "workout with the Standard Model lagrangian" | 2005-10-25 |
This book is about the experimental facts and the theoretical principles that lead to the construction of the Standard Model lagrangian. It is NOT about calculating scattering crossections. Some of the problems ask you to calculate decay rates but only at tree level and the fields are treated like classical fields not operators, with the exception that the fermionic fields anticommute. There is a 12-page chapter on quantizing the fields and renormalization but I find it rather sketchy so don't expect to understand a lot from it if you don't already know it. You should have some background in varying lagrangians otherwise the book will frequently seem difficult to you. The authors obtain symmetry currents corresponding to a symmetry of the lagrangian not in the standard way of Noether's theorem. Their method is entirely correct but it took me long time to understand because they didn't explain it with enough details the first time they used it (section 7.1, page 65). I think that will throw off the horse many readers. The style is wonderfully concise which makes the logical structure easier to follow and there isn't the usual fluff `to motivate' things that are simply put guesses like the principle of local gauge invariance. On the other hand, some places definitely need more detailed explanations like signs of certain quantities or the symmetry currents I mentioned above. The treatment of the Dirac equation and spinors is the least messy I've seen. The way they obtain the nonrelativistic limit of the Dirac equation with EM field is again the best and least messy I've seen. The book has nice appendix on the groups of the Standard Model which covers what you need to know about SO(3), SU(2) and SU(3) in a very efficient way. There are about 5 problems after each chapter most of which have a solution outline at the end of the book. Things I understood from this book: -- why time reversal, space inversion and charge conjugation of fields are defined in a way that previously seemed to me quite arbitrary -- how demanding local gauge invariance necessitates introduction of gauge fields which leads to interaction terms -- how local gauge invariance can't be proven, it's just a guess that has worked so far hence it's called `principle' (my own interpretation) -- global and local symmetry breaking, Goldstone bosons and Higgs boson -- how the Lagrangian densities of the electroweak and strong interactions were constructed from the experimental input by demanding local gauge invariance and guessing the symmetry group to be SU(2) and SU(3) correspondingly -- what's Kobayashi-Maskawa matrix that mixes the quark fields and how it arises -- how symmetries of the lagrangian density lead to conservation numbers -- how neglecting some terms in the lagrangian leads to effective lagrangian and effective theory -- how to work with the terms in the QCD lagrangian where different matrices multiply different indices | ||
 | Gauge Theories in Particle Physics: A Practical Introduction (Graduate Student Series in Physics) | |
| "more understandable QFT for beginners" | 2005-09-17 |
The 3rd edition of that book clarified to a degree the fog left in my mind by a two-semester QFT course. The book is better suited for beginners than Peskin & Shroeder, Mandl & Show or Lahiri & Pal simply because it senses better the difficult points for beginners and tries to explain them at lower level. It focuses on the main concepts and doesn't try to `cover broad material in shortest time' or get into extreme computational technicalities totally irrelevant to beginners. The correct historical perspective of many ideas is given and the important historical papers are cited. The theory is frequently compared to the experimental results. Violin string is used as a prototype of a continuous system described by a classical field which is the first field quantized later. The book develops physical intuition showing how a scattering process can be analyzed in full QED (all fields are operators), in semiclassical approximation (all fields are operators except the EM field) or using the lowest level wavefunction approximation (all fields are treated like wave functions just like scattering in nonrelativistic QM) often getting the same result (see chapter 8). Important concepts like Feynman diagrams and Renormalization of a theory are first explored in a simple theoretical playground - a hypothetical `ABC theory' of three massive scalar fields with an interaction ABC term - and later discussed again in the case of QED with all the complications like fermions and Electromagnetic gauge field. Topics discussed include gauge invariance principle; relativistic field equations describing free particles like Klein-Gordon and Dirac; Feynman interpretation of the negative energy solutions of Dirac eq. (no its not `antiparticle going back in time'); Dirac equation with EM field; Lagrangian and Hamiltonian densities for continuous systems; quantization of free fields like KG (real and complex scalar), Dirac and Electromagnetic field [the quantization is by postulating commutators/anticommutators, no path integrals]; Normal ordering of operators; Interaction picture for interacting fields, Time ordering of operators, Dyson expansion of the S matrix; Wick's theorem; scattering processes in QED at tree level; Ward identity; form factors for scattering from non point particle; parton model, Bjorken scaling; diagrams with loops, regularization and renormalization of ultraviolet divergences in QED. It took me a month and a half to read the book and solve all problems (10 problems per chapter on average). The problems are exactly the ones every beginner should solve and usually revolve about filling in details from the text or proving statements in the text. Solving them is usually easy with a few exceptions and teaches you the typical computational tricks of the trade. You have to know quantum mechanics (at least have seen scattering theory) and special relativity. You have to at least have heard of Green function and contour integration in the complex plane. The book provides nice appendices about all these. Not everything is crystal clear in that book, sometimes it took me a few days for an idea to sink in or I understood some paragraphs only after I read the whole book. Other ideas I did not understand at all. Sometimes it's hard to tell what they are trying to say although they say it several times from different angles ... The authors should work on expressing an idea in a direct succinct way once and for all instead of repeating several fuzzy versions of it. Overall that book made me understand MUCH more than a regular QFT course and I highly recommend it as a prep for such a course. | ||
 | Olay Regenerist Daily Regenerating Serum | |
 | "OVERPRICED silicone based MAKEUP" | 2005-04-27 |
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Let's be objective and make difference between MAKEUP effects (the skin LOOKS good) and a real IMPROVEMENT of your skin (erasing them bad wrinkles :). The MAKEUP effect that most consumers describe (silky smooth feel, glow, even tone, visual minimization of wrinkles) is due to the silicones the product contains NOT TO MATRIXYL (the comersial name of the active amino-peptide) - it will take more than a day and more than a few weeks to erase a wrinkle by stimulating collagen production if Matrixyl has any effect at all ... Some consumers report no real reduction of wrinkles after 6 months of usage. Most consumers report VISUAL reduction of wrinkles while the product is still on their face which is kind of not very objective - try to wash it off, wait a few hours for the skin to normalize and THEN look if the crow's feet are smaller .... The product really makes your skin softer cause it decreases water evaporation and it really makes your skin look younger cause it fills in small wrinkles and mattifies the skin surface - but so does every good makeup :) The difference is that silicones are really good makeup - nobody could tell you have them on your face - the look is completely natural. Paying $18 / oz (retail price, its cheaper on amazon but you have to pay shipping price) for a silicone makeup is a little steep for me provided that there are cheaper products on the market that will make your skin look equally good cause they contain the same silicone base even better - try Monistat soothing care - chafing relief powder gel 1.5 OZ, $7 at CVS. I have been using Matrixyl for 6 months in my own formulations (without silicones) and frankly speaking haven't noticed any improvement in my crows feet or the lines on my forehead. Currently there is only one study of the effects of Matrixyl conducted by Sederma - the MANIFACTURER of Matrixyl which makes me quite suspicious about the whole story .... | ||
 | Spacetime and Geometry: An Introduction to General Relativity | |
 | "good math chapters, not at beginner's level after that" | 2005-03-07 |
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I had a course based on that book and I've read chapters 1-6 (out of 9 chapters total) plus all the appendices. Also, I've solved some of the problems. Please keep in mind my review is from a beginner point of veiw. Readers more experienced in GR may feel different but that book is supposedly written for beginners right? The math chapters 2 and 3 are worth reading because they will teach you tensor analysis on manifolds in much clearer way than other books. The book makes a clear distinction between assumptions, choices (like working with a metric compatible connection), or derived facts. It is nice that the book makes a difference between a Christoffel connection and a generic connection. The appendices are worth reading too cause they will give you a feeling for some new to you math necessary for GR like pullbacks, Lie Derivatives, hypersurfaces etc. Chapter 4 is worth reading too cause it makes clear that Einstein's equations are just the simplest guess out of many other possibilities. Also it shows how we generalize physical laws from special relativity to GR making it clear our choices are the simplest ones but not the only ones possible. The chapters after that discuss applications of GR like black holes, gravitational radiation, cosmology etc. Of these, I've read only the black holes chapters 5 and 6 and I wasn't able to understand 100% what was goin on. The problem was that the book uses concepts that you still don't quite understand if you are a beginner like 'spacelike singularity' or 'conformal diagrams'. That is informative but you won't be able to use these concepts to solve a real physical problem. There are problems after each chapter but not the necessary beginners problems that increase your conceptual understanding of the theory. Instead, some of the problems are just tedious algebra of type 'find the curvature for some general form of the metric' for which specialists in the field use symbolic programs like Mathematica. Solving these by hand proves that you can take derivatives and you are a mazochist but not that you understand GR. If you are a beginner like me, you should read the math chapters and all appendices of Carroll's book plus chapter 4. Then you should read a real book for beginners with a lot of examples how to apply GR in real calculations and how to understand it. For that I recommend James Hartle's "Gravity: An Introduction to Einstein's General Relativity" and Bernard Schutz's "A first course in General Relativity". After that hopefully you will understand the rest of Carroll's book better. My experience was that often I had to read Hartle's book in order to understand and solve a problem in Carroll's book. | ||
 | Casio Exilim EX-S100 3.2MP Digital Camera with 2.8x Optical Zoom | |
| "not good in low light (indoor without flash or at night)" | 2005-03-06 |
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I tested the cam for about two weeks. Overall this cam has many features but the performance in low light without flash is not good. I will mention only specific things that are not in the other reviews: pros: -- good outdoor daylight pics [all digital cams above $150 are good enough in this area] -- good pics with flash -- can use digital zoom during movie -- can use continuous focus during movie but the sound of the moving lens will be recorded also -- has an alignment grid that helps a lot if you frequently shoot text (can be turned on and off). It helps to check if the cam is exactly parallel to the text. -- lack of barrell distortion when shooting text in macro mode (a rectangle doesn't look 'swallen') cons: -- noisy pics indoors in incandescent light without flash -- noisy videos indoors in incandescent light -- problems focusing indoors without flash even during the day | ||
 | Canon PowerShot A510 3.2MP Digital Camera with 4x Optical Zoom | |
| "good package at low price" | 2005-03-06 |
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If you were wondering which one to buy - Canon A510 or Canon SD200 (the ultracompact), here is my comparison below. The bottom line is that A510 takes a little bit sharper pics but a little bit noisier in low light than SD200. ++ A510 is about $50 cheaper ++ A510 has manual controls for focus, aperture and exposure; SD200 doesn't ++ A510 doesn't have fuzzy pic corners or purple fringing; SD200 has them ++ A510 uses two AA bateries (rechargeable or not); SD200 uses rechargeable lithium-ion battery (NB-4L) -- A510 uses the older processor DIGIC I; SD200 uses DIGIC II, hence the differences below ... -- A510 needs bigger time to auto-focus than SD200 but it wasn't a problem for me -- A510 records movies with limited length; SD200 records till the memory card is full -- A510 has worse noise reduction than SD200 in low light conditions (more pixel noise in incandescent light without flash, including the movie mode) -- A510 doesn't have 'indoors' white balance; SD200 has it. A510 has an 'indoors' shooting scene but you can't use the manual controls in a scene mode. | ||
 | Gravitation (Physics Series) | |
| "good reference for advanced, NOT A LOGICAL INTRO to GR" | 2005-02-02 |
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This book is known as the 'bible' of General Relativity or 'MTW'. People with different preparation will perceive MTW in different ways: The beginners in GR very often will feel that the book is a good reference and shows 'properties' of the defined objects instead of explaining the logical necessity of demanding such properties. My first course in GR was based on that book and although I learned some 'index gymnastics' from it, very often I had questions of the type 'where does this come from, why is it defined this way'. Often I would read about something like 'affine parameter' and I would not understand its importance at all. For beginners I recommend the books from J.Hartle, B. Schutz, and S. Carroll in order of increasing abstraction. I am currently in the middle of course based on the Carroll's book and I understand things I have never ever been able to understand from the 'bible' like the fact that we may define different connections but only one of them is metric compatible and we CHOOSE to work with it, or that we CHOOSE to work with a torsion free connection, or that reparametrizing a geodesic may not give you back a geodesic (in relation to the affine parameter remark above) ... Such facts are either not clearly spelled in the 'bible' or they are digged in somewhere 300 pages away ... Once you are past your first (or better second) course in GR, that book will be an invaluable reference for you with plenty of examples how to apply different computational and theoretical techniques in GR. The reviewers that give it high rating are obviously either experienced in the field or are begginners that value a book only because of the well-known authours. The book is really a titanic effort to compile all relevant pieces of info into one thick volume BUT PLEASE PLEASE think carefully before you recommend it for INTRODUCTION to General Relativity !!! | ||
 | Canon PowerShot SD200 Digital Camera | |
| "very good pics, slightly blurry corners and purple fringing" | 2005-01-27 |
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I had the cam for two months. The bottom line: Buy this cam if you need a super compact cam, that takes very good quality pictures that are well focused, correctly exposed, with accurate colors and noiseless even at night and indoors without flash. If purple fringing and a little blurriness in the corners matters to you then look elsewhere. Outdoor pics (daylight): Very good quality pics except pronounced purple fringing usually at the edge of a dark object (a tree branch) on a bright background (the sky). Most people won't notice it unless you tell them. Outdoor pics (night, no flash, on timer): The flash won't help you here for distant objects so I didn't use it. To my surprise the cam took reasonable pics of a very dark street (30% of the trials the pics were well focused wihtout noise, 70% were defocused). Instead of using a tripod I set the cam on timer to reduce hand-shake. The pic looked very much like the reality. The shutter speed was 1/10 of a second, the Iso was probably 400 (for some reason the pic info doesn't contain the ISO). Indoor pics (daytime, no flash, on timer): The cam sensor seems to be sensitive enough and handles low light situation well - without noise and 50% of the pics were well focused. I took focused pics at shutter speed 1/8 of a second, without a tripod - to reduce the effect of hand-shake I used the timer. I didn't use the flash indoors in daylight since that produces too much shiny faces and it doesn't look very natural. Night pics (with flash): I took a well focused and exposed pic of a friend of mine in a bar. The flash is strong enough for 3 meters maybe and the color rendition was accurate. Burst mode (with a fast memory card, the cam takes pic after pic till you hold the shutter pressed): NEWS FLASH for you - the cam focuses only at the first pic and the following pics are taken with the same focus, shutter and aperture. It is not clear to me then why that is considered usefull???? Movie mode: The highest resolution 640x480 produces super big files so you really need a Gigabyte memory to use it. The sound is recorded with the video. Another NEWS FLASH for you - the camera focuses when taking the first movie frame and then it keeps that focus constant. That means dear Willie that the object will get out of focus if it moves around. The defocusing is not as bad as it would be in taking pictures for example (I guess the cam keeps the depth of field big by closing the aperture or something). I understand that they couldn't set up a continuous focus because the sound from the zooming lense will destroy the soundtrack. Macro mode: I used the cam to copy pages from books. As most of the professional reviews point out, the camera produces pics with slightly blurry corners. That doesn't matter in everyday point and shoot photography of people or houses in the center of the frame but for shooting text it matters. The corners of the text were still readable but I decided to try to find a compact camera that will handle the corners better. All super compact cameras are expected to have that problem due to their small lenses. Note: The higher pixel model Powershot SD300 is not only more expensive but will also have more purple fringing and blurry corners (as the professional reviews on www.dcreview.com show). More pixels doesn't mean better quality as many people think!. More often than not it is quite the opposite! | ||
 | Exploring Black Holes: Introduction to General Relativity | |
| "teaches calculations, some statements without justification" | 2005-01-13 |
| I am a graduate student in physics and I like reading books for undergraduates like this one. I've learned more from this book than from the 'bible' MTW or from the usual superficial graduate courses in GR that boil down to 'index gymnastics' whithout conceptual depth.
The dominant theme in the book is spherically symmetric noncharged and nonrotating black holes described by the Schwartzschild metric. Only the last two projects deal with rotating black holes and cosmological metrics. The book covers only a small application chapter of GR so don't expect to see the Einstein equations or tensors (there isn't a single one). It took me a month to read the book and do all the exercises which I found easy most of the time since they come with pretty detailed instructions how to solve them. You will need to know a little special relativity and calculus so it is completely within the reach of an undergrad. The Schwartzschild metric is stated without derivation. Then you are introduced to 3 different observers around the black hole and their measurements. You will use a variational principle called in the book 'Principle of extremal aging', to derive the orbits of bodies and light rays around the black hole and constants of motion like energy and angular momentum. The radial motion is tackled through 'effective potential', the angular motion through the angular momentum. At the end of the book you will begin to understand how to tackle a general metric: how to interpret its coordinates in terms of measurements performed by different observers, how the constants of motions are connected to symmetries in the metric, how to get the constants of motion with the variational principle and so on... Besides all that, you will learn a bunch of wonderfull facts about black holes that will make you a star at a nerd's party :) Can you cross the horizon and what is seen by different observers, the time from the moment your body feels uncomfortable till the moment you reach the center of the black hole, how the night sky looks close to the black hole and so on. Some of the projects in the book calculate the hystorical experimental proofs of GR: bending of light near sun, precession of mercury's orbit and so on. The projects contain queries that you have to fill in reading the text. The solutions of these are usually shorter than the questions themselves :) My only objection is that sometimes the book makes statements without justification. For example, it is enogh to say that the principle of extremal aging like every principle is a statement in agreement with the experiment that can't be proven, we just know it works but don't know why. Instead of explaining that, the book states the principle several times wasting paper to my opinion and you still don't understand where that principle comes from. Repeating statements without proper explanation is equivalent to brain-washing and just makes the text unnecessary bulky and inefficient. For sins like that I gave it 4/5. Keep in mind I am a pretty demanding reader and I give 5/5 only to masterpieces like some books of David Griffiths where you can see the authour applied great effort to streamline the logic and clearly justify it to the reader. | ||
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