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• Is there really such a thing as "being good at math"?

  - by thezhaba

  Aside from gifted individuals able to perform complex calculations in their head, I'm wondering if proficiency in mathematics, namely calculus and algebra, has really got to do with one's natural inclination towards sciences, if you can put it that way. A number of students in my calculus course pick up material in seemingly no time whereas I, personally, have to spend time thinking about and understanding most concepts. Even then, if a question that requires a bit more 'imagination' comes up I don't always recognize the concepts behind it, as is the case with calculus proofs, for instance. Nevertheless, I refuse to believe that I'm simply not made for it. I do very well in programming and software engineering courses where a lot of students struggle. At first I could not grasp what they found to be so difficult, but eventually I realized that having previous programming experience is a great asset -- once I've seen and made practical use of the programming concepts learning about them in depth in an academic setting became much easier as I have then already seen their use "in the wild". I suppose I'm hoping that something similar happens with mathematics -- perhaps once the practical idea behind a concept (which authors of textbooks sure do a great job of concealing..) is evident, understanding the seemingly dry and symbolic ideas and proofs would be more obvious? I'm really not sure. All I'm sure of is I'd like to get better at calculus, but I don't yet understand why some of us pick it up easily while others have to spend considerable amounts of time on it and still not have complete understanding if an unusual problem is given.

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• getting number of hours until the next event

  - by Andrew Heath

  I've got a table with this data: [ID] [event_name] [last_event] 1 stats 2011-01-01 01:47:32 last_event is a timestamp. The event occurs every 48 hours (it's a cron job). I'd like to show my users the number of hours until the event executes again. So far I've got: SELECT (lastFinish + INTERVAL 48 HOUR) FROM `cron_status` which gives me the exact time and date of the next occurence: 2011-01-03 01:47:32. So I figured if I subtracted the current datetime... SELECT ((lastFinish + INTERVAL 48 HOUR) - SYSDATE()) FROM `cron_status` which (I think?) gives me the difference in unix time: 1980015. But if I divide that by 3600 to convert the seconds to hours... SELECT (((lastFinish + INTERVAL 48 HOUR) - SYSDATE())/3600) FROM `cron_status` I get numbers an order of magnitude too high: 549.99. Where am I going wrong? The target is returning the number of hours until the next execution. Thank you!

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• What are real-world examples of Gradle's dependency graph?

  - by Michael Easter

  As noted in the documentation, Gradle uses a directed acyclic graph (DAG) to build a dependency graph. From my understanding, having separate cycles for evaluation and execution is a major feature for a build tool. e.g. The Gradle doc states that this enables some features that would otherwise be impossible. I'm interested in real-world examples that illustrate the power of this feature. What are some use-cases for which a dependency graph is important? I'm especially interested in personal stories from the field, whether with Gradle or a similarly equipped tool. I am making this 'community wiki' from the outset, as it will be difficult to assess a 'correct' answer.

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• [PHP] - Lowering script memory usage in a "big" file creation

  - by Riccardo

  Hi there people, it looks like I'm facing a typical memory outage problem when using a PHP script. The script, originally developed by another person, serves as an XML sitemap creator, and on large websites uses quite a lot of memory. I thought that the problem was related due to an algorithm holding data in memory until the job was done, but digging into the code I have discovered that the script works in this way: open file in output (will contain XML sitemap entries) in the loop: ---- for each entry to be added in sitemap, do fwrite close file end Although there are no huge arrays or variables being kept in memory, this technique uses a lot of memory. I thought that maybe PHP was buffering under the hood the fwrites and "flushing" data at the end of the script, so I have modified the code to close and open the file every Nth record, but the memory usage is still the same.... I'm debugging the script on my computer and watching memory usage: while script execution runs, memory allocation grows. Is there a particular technique to instruct PHP to free unsed memory, to force flushing buffers if any? Thanks

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• Firefox extension js object initialization

  - by Michael

  Note: this is about Firefox extension, not a js general question. In Firefox extension project I need my javascript object to be initialized just once per Firefox window. Otherwise each time I open my window a new timers will be engaged, new properties will be used, so everything will start from scratch. hope example below will demystify my question :) var StupidExtension { statusBarValue: "Not Initialized Yet", startup: function () { ... // Show statusBarValue in Status Bar Panel }, initTimerToRetrieveStatusBarValueFromNetwork: function () { ... } } so each time you hit Ctrl+N a new window you will see "Not Initialized Yet" and then new timer will be fired, so after some time it retrieve data from network you will see value also on second window and so on. Ideally would be to have just a single timer function running and updating all status bar panels in all Firefox windows. Of course I can do some caching, like saving the value in prefs or some other storage, then show it from there. But I feel like this is artificial. So the question will be is there "native" technique of making static some parts of the object among all Firefox window instances?

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• File.Exists("SDF File Path") returns a FALSE when run through Unit tests even though it exists in th

  - by shiva-hv

  I am writing Unit tests for a Windows Project. The Executable project on the Client Side of this Windows Project has a code File.Exists("LanguageLookups.sdf") which is used to check and return a Bool if the sdf file exists in the Execution Directory or not. But when i execute the same piece of Code through a Unit test; The code File.Exists("LanguageLookups.sdf") returns a FALSE. Its not able to find this SDF File. Can anybody help me on this?

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• Forcing a templated object to construct from a pointer

  - by SalamiArmi

  I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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• How are developers using source control, I am trying to find the most efficient way to do source con

  - by RJ

  I work in a group of 4 .Net developers. We rarely work on the same project at the same time but it does happen from time to time.We use TFS for source control. My most recent example is a project I just placed into production last night that included 2 WCF services and a web application front end. I worked out of a branch called "prod" because the application is brand new and has never seen the light of day. Now that the project is live, I need to branch off the prod branch for features, bugs, etc... So what is the best way to do this? Do I simple create a new branch and sort of archive the old branch and never use it again? Do I branch off and then merge my branch changes back into the prod branch when I want to deploy to production? And what about the file and assembly version. They are currently at 1.0.0.0. When do they change and why? If I fix a small bug, which number changes if any? If I add a feature, which number changes if any? What I am looking for is what you have found to be the best way to efficiently manage source control. Most places I have worked always seem to bang heads with the source control system in on way or another and I would just like to find out what you have found that works the best.

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• Improve Efficiency in Array comparison in Ruby

  - by user2985025

  Hi I am working on Ruby /cucumber and have an requirement to develop a comparison module/program to compare two files. Below are the requirements The project is a migration project . Data from one application is moved to another Need to compare the data from the existing application against the new ones. Solution : I have developed a comparison engine in Ruby for the above requirement. a) Get the data, de duplicated and sorted from both the DB's b) Put the data in a text file with "||" as delimiter c) Use the key columns (number) that provides a unique record in the db to compare the two files For ex File1 has 1,2,3,4,5,6 and file2 has 1,2,3,4,5,7 and the columns 1,2,3,4,5 are key columns. I use these key columns and compare 6 and 7 which results in a fail. Issue : The major issue we are facing here is if the mismatches are more than 70% for 100,000 records or more the comparison time is large. If the mismatches are less than 40% then comparison time is ok. Diff and Diff -LCS will not work in this case because we need key columns to arrive at accurate data comparison between two applications. Is there any other method to efficiently reduce the time if the mismatches are more thatn 70% for 100,000 records or more. Thanks

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• Checking if an SSH tunnel is up and running

  - by Jarmund

  I have a perl script which, when destilled a bit, looks like this: my $randport = int(10000 + rand(1000)); # Random port as other scripts like this run at the same time my $localip = '192.168.100.' . ($port - 4000); # Don't ask... backwards compatibility system("ssh -NL $randport:$localip:23 root\@$ip -o ConnectTimeout=60 -i somekey &"); # create the tunnel in the background sleep 10; # Give the tunnel some time to come up # Create the telnet object my $telnet = new Net::Telnet( Timeout => 10, Host => 'localhost', Port => $randport, Telnetmode => 0, Errmode => \&fail, ); # SNIPPED... a bunch of parsing data from $telnet The thing is that the target $ip is on a link with very unpredictable bandwidth, so the tunnel might come up right away, it might take a while, it might not come up at all. So a sleep is necessary to give the tunnel some time to get up and running. So the question is: How can i test if the tunnel is up and running? 10 seconds is a really undesirable delay if the tunnel comes up straight away. Ideally, i would like to check if it's up and continue with creating the telnet object once it is, to a maximum of, say, 30 seconds.

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• How to save event handlers, when we set new html for element?

  - by Kai

  I have simple html markup: <div id="cont">Some text here <div class="wrap" style="border: 1px solid black;display: inline;"> block element here </div> and another text</div> And jQuery code: $(function(){ $(".wrap").click(function(){ $("#cont").html($("#cont").html().replace(/text/g, "letter")); alert("Click!"); }); $("#d1").click(function(){ alert("#d1 clicked!"); }); }); I expect that click event will be fire any time you clicked by the #d1 div, but when we clicked by .wrap it neve fire again. I understand why it has such behavior, but how to solve it? In my code I can't set click event for #d1 after $("#cont").html($("#cont").html().replace(/text/g, "letter")) because I don't now at execution time if event was set. You can try example on JSBin

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• Communication between lexer and parser

  - by FredOverflow

  Every time I write a simple lexer and parser, I stumble upon the same question: how should the lexer and the parser communicate? I see four different approaches: The lexer eagerly converts the entire input string into a vector of tokens. Once this is done, the vector is fed to the parser which converts it into a tree. This is by far the simplest solution to implement, but since all tokens are stored in memory, it wastes a lot of space. Each time the lexer finds a token, it invokes a function on the parser, passing the current token. In my experience, this only works if the parser can naturally be implemented as a state machine like LALR parsers. By contrast, I don't think it would work at all for recursive descent parsers. Each time the parser needs a token, it asks the lexer for the next one. This is very easy to implement in C# due to the yield keyword, but quite hard in C++ which doesn't have it. The lexer and parser communicate through an asynchronous queue. This is commonly known under the title "producer/consumer", and it should simplify the communication between the lexer and the parser a lot. Does it also outperform the other solutions on multicores? Or is lexing too trivial? Is my analysis sound? Are there other approaches I haven't thought of? What is used in real-world compilers? It would be really cool if compiler writers like Eric Lippert could shed some light on this issue.

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• MySQL 5.5.8 Gets Periodic Lag

  - by CYREX

  Am using MySQL 5.5.8 on an Ubuntu system and every X amount of time it creates a huge lag that lasts a couple of seconds. Then all goes back to normal until the next lag. The time period varies but it looks like it happen periodically. Am using InnoDB. It is like hiccups in the MySQL. What could be creating this sort of periodic problem. Do not have any cron jobs or process running every time the X period happens. The X period could be between 30 minutes to 2 hours. So for example it could happen every 30 minutes for the next 12 hours or it could happen every 2 hours for the next 8 hours. key_buffer_size = 256M max_allowed_packet = 1M table_cache = 1024 table_open_cache = 1024 sort_buffer_size = 2M read_buffer_size = 2M read_rnd_buffer_size = 4M myisam_sort_buffer_size = 32M thread_cache_size = 128 query_cache_size= 128M log-slow-queries = slow.log long_query_time = 5 log-queries-not-using-indexes # Try number of CPU's*2 for thread_concurrency thread_concurrency = 4 max_connections=512 #innodb_data_file_path = ibdata1:10M:autoextend #innodb_log_group_home_dir = /usr/local/mysql/data # You can set .._buffer_pool_size up to 50 - 80 % # of RAM but beware of setting memory usage too high innodb_buffer_pool_size = 1G #innodb_additional_mem_pool_size = 20M # Set .._log_file_size to 25 % of buffer pool size #innodb_log_file_size = 64M #innodb_log_buffer_size = 8M #innodb_flush_log_at_trx_commit = 0 #innodb_lock_wait_timeout = 50 [mysqldump] quick max_allowed_packet = 16M [myisamchk] key_buffer_size = 64M sort_buffer_size = 64M read_buffer = 2M write_buffer = 2M There are about 200+ tables divided in 3 databases. The most written too is in InnoDB. The other ones are more read. Several of the tables in the InnoDB have more than 2 million records. The other databases top at about 400 thousand records and do not change so often. The PC is a Core 2 Duo 8400 with 4GB RAM, 32Bit Ubuntu.

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• use of ajax in django problem with the code

  - by tazim

  I am new to ajax and using Django for web development. Now My Template contains : sample.html <html> <body> <script language="javascript" type="text/javascript"> //Browser Support Code function ajaxFunction(){ var ajaxRequest; // The variable that makes Ajax possible! try{ // Opera 8.0+, Firefox, Safari ajaxRequest = new XMLHttpRequest(); } catch (e){ // Internet Explorer Browsers try{ ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try{ ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP"); } catch (e){ // Something went wrong alert("Your browser broke!"); return false; } } } // Create a function that will receive data sent from the server ajaxRequest.onreadystatechange = function(){ if(ajaxRequest.readyState == 4){ document.myForm.time.value = ajaxRequest.responseText; } } ajaxRequest.open("GET", "/showtime/", true); ajaxRequest.send(null); } </script> <form name='myForm'> Name: <input type='text' onBlur="ajaxFunction();" name='username' /> <br /> Time: <input type='text' name='time' /> </form> </body> </html> In views.py my function is : def showtime(request): string = "Ajax Application" data = {"string" : string} pprint (data) return render_to_response("sample.html",data) Now, The output is not as expected . The template does not receives the response sent by the server What is wrong with the code ?

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• Higher speed options for executing very large (20 GB) .sql file in MySQL

  - by Jonogan

  My firm was delivered a 20+ GB .sql file in reponse to a request for data from the gov't. I don't have many options for getting the data in a different format, so I need options for how to import it in a reasonable amount of time. I'm running it on a high end server (Win 2008 64bit, MySQL 5.1) using Navicat's batch execution tool. It's been running for 14 hours and shows no signs of being near completion. Does anyone know of any higher speed options for such a transaction? Or is this what I should expect given the large file size? Thanks

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• different thread accessing MemoryStream

  - by Wayne

  There's a bit of code which writes data to a MemoryStream object directly into it's data buffer by calling GetBuffer(). It also uses and updates the Position and SetLength() properties appropriately. This code works purposes 99.9999% of the time. Literally. Only every so many 100,000's of iterations it will barf. The specific problem is that the memory.Position property suddenly returns zero instead of the appropriate value. However, code was added that checks for the 0 and throws an exception which include log of the MemoryStream properties like Position and Length in a separate method. Those return the correct value. Further addition shows that when this rare condition occurs, the memory.Position only has zero inside this particular method. Okay. Obviously, this must be a threading issue. But this code is well locked. However, the nature of this software is that it's organized by "tasks" with a scheduler and so any one of several actual O/S thread may run this code at any give time--but never more than one at a time. So it's my guess that ordinarily it so happens that the same thread keeps getting used for this method and then on a rare occasion a different thread get used. Then due to compiler optimizations, the different thread never gets the correct value. It gets a "stale" value. Ordinarily in a situation like this I would apply a "volatile" keyword to the variable in question. But that (those) variables are inside the MemoryStream object. Does anyone have any other idea? Or does this mean we have to implement our own MemoryStream object? (Just like we end up having to do with practically every collection in .NET?) It's a shame to have such an awesome platform as .NET and have virtually the entire system useless as-is for seriously parallelized applications. If I'm wrong or you have other ideas, please advise. Sincerely, Wayne

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• Build Pipelining and Continuous Integration with Maven and Hudson

  - by Brandon

  Currently the my team is considering splitting our single CI build process into a more streamlined multi-stage process to speed up basic build feedback and isolate different ci concerns. The idea we had was to have each stage exist in Hudson as a different build with the correct maven goal or maven plugin execution, then chain them together using the post-build hooks of Hudson. However to my knowledge, Maven as a build tool mandates that any lifecycle phase which is performed automatically builds every preceding lifecycle phase. This presents a number of problems the most significant of which is that maven is recreating the build resources with each distinct call and not using those of the previous stage. This not only breaks the consistency of the build lifecycle but has much more unnecessary processing overhead. Is there a way to accomplish pipelining with CI using Maven? Assuming there is, is there a way to let Hudson know to use those resources built from the previous stage in the next one?

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• [C#] how to do Exception Handling & Tracing

  - by shrimpy

  Hi all, i am reading some C# books, and got some exercise don't know how to do, or not sure what does the question mean. Problem: After working for a company for some time, your skills as a knowledgeable developer are recognized, and you are given the task of “policing” the implementation of exception handling and tracing in the source code (C#) for an enterprise application that is under constant incremental development. The two goals set by the product architect are: 100% of methods in the entire application must have at least a standard exception handler, using try/catch/finally blocks; more complex methods must also have additional exception handling for specific exceptions All control flow code can optionally write “tracing” information to assist in debugging and instrumentation of the application at run-time in situations where traditional debuggers are not available (eg. on staging and production servers). (i am not quite understand these criterias, i came from the java world, java has two kind of exception, check and unchecked exception. Developer must handle checked exception, and do logging. about unchecked exception, still do logging maybe, but most of the time we just throw it. however here comes to C#, what should i do????) Question for Problem: List rules you would create for the development team to follow, and the ways in which you would enforce rules, to achieve these goals. How would you go about ensuring that all existing code complies with the rules specified by the product architect; in particular, what considerations would impact your planning for the work to ensure all existing code complies?

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• How to load an image in matlab from java

  - by Ian

  Basically I am trying to create a little program that will allow me to make calls in matlab from a jave GUI It's mainly going to be used for image manipulation and deblurring but I am struggling to find a way that will effectively give me full matlab control from the java end I am hoping to have it work like so: { //create matlab execution call String loadImage = " image1 = imread ('imageOnComputer.jpg'); "; //send instruction to matlab and save the path to it so java can //use the newly created variable resultingVariablePath = java.sendInstructionToMatlab(loadImage); //display on the screen java.displayImage(resultingVariablePath); } Basically I am just trying to find out if there is a plugin for matlab (or some java package) that will grant you (pretty much) full control over matlab.

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• FFT and IFFT on 3D matrix (Matlab)

  - by SteffenDM

  I have a movie with 70 grayscale frames in MATLAB. I have put them in a 3-D matrix, so the dimensions are X, Y and time. I want to determine the frequencies in the time dimension, so I have to calculate the FFT for every point in the 3rd dimension. This is not a problem but I have to return the images to the original form with ifft. In a normal situation this would be true: X = ifft(fft(X)), but this is not the case it seems in MATLAB when you work with multidimensional data. This is the code I use: for i = 1:length y(:, :, i) = [img1{i, level}]; %# take each picture from an cell array and put it end %# and put it in 3D array y2 = ifft(fft(y, NFFT,3), NFFT, 3); %# NFFT = 128, the 3 is the dimension in which i want %# to calculate the FFT and IFFT y is 480x640x70, so there are 70 images of 640x480 pixels. If I use only fft, y2 is 480x640x128 (this is normal because we want 128 points with NFFT). If I use fft and ifft, y2 is 480x640x128 pixels. This is not normal, the 128 should be 70 again. I tried to do it in just one dimension by using 2 for loops and this works fine. The for loops take to much time, though.

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• Ruby and Rails Async

  - by Edijs Petersons

  I need to perform long-running operation in ruby/rails asynchronously. Googling around one of the options I find is Sidekiq. class WeeklyReportWorker include Sidekiq::Worker def perform(user, product, year = Time.now.year, week = Date.today.cweek) report = WeeklyReport.build(user, product, year, week) report.save end end # call WeeklyReportWorker.perform_async('user', 'product') Everything works great! But there is a problem. If I keep calling this async method every few seconds, but the actual time heavy operation performs is one minute things won't work. Let me put it in example. 5.times { WeeklyReportWorker.perform_async('user', 'product') } Now my heavy operation will be performed 5 times. Optimally it should have performed only once or twice depending on whether execution of first operaton started before 5th async call was made. Do you have tips how to solve it?

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• Printing and exporting from Crystal Reports Viewer throws error

  - by MAW74656

  I'm using the .net Crystal Reports viewer to display a report. This works properly, but when I click on the print option, and then click "OK" on the options popup, I get the following error: Access is denied. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Runtime.InteropServices.COMException: Access is denied. And the same thing when I try to export. I'm running this on the Visual Studio development server, VS2008. What can I do to correct this?

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• iphone app hangs in AppDelegate (?)

  - by d_CFO

  No nib/IB, so I've inserted "myAppDelegate" in main and deleted the reference to main.xib in info.plist. Debug continues nicely through all five tab controllers; they seem to have gotten properly loaded into the nav controller. In fact, control passes out of the last "}" in applicationDidFinishLaunching. But there was no (visible) response back at [window addSubview:[tabBarController view]]; and [window makeKeyAndVisible]; statements, much less to the loadView within the first tab (program execution never gets there). The last line is, UIApplication _performInitializationWithURL:sourceBundleID:]. I missed a step? I executed a step improperly?

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• Microsoft AntiXSS in Medium Trust :Error

  - by aramugam

  I want to include Microsoft AntiXss V1.5 library on my live site running in a medium trust setting.However, I got an error something like: Required permissions cannot be acquired. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Security.Policy.PolicyException: Required permissions cannot be acquired. I tried this in full trust setting on my development machine and everything works good.Looks like this will run only in full trust configuration......Does anybody knows a solution or workaround for this?

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• How do I remotely obtain a system's network shares and connections?

  - by Mick

  I'm looking for a way to obtain information similar to the following console applications, remotely: net use net share netstat -ano However, I need to be able to do this without running a 3rd party application on the system. This effectively rules out using psexec to execute the command remotely, because psexec would then be installed as a service. I should add that I have administrative credentials on the remote system. I've considered using WMI's remote execution ability, but that requires me to write output to a file and then retrieve it. It's possible, but I'd like to know if anyone has a better way. I am using Delphi 2010.

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