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• Clustering and custom applications

  - by Ahmed ilyas

  I was not entirely sure what tags to put but hope this is ok. This is just a general question in regards to clustering and applications: so lets say we have a clustered environment setup. We cluster SQL Server (I dont know exactly how its done but lets just say its been done for the sake of argument). Now if a website or application is trying to access that database for read/write (say an ASP.NET app or a C# Winforms app) and during that time SQL goes down - it takes a couple of minutes for the clustering failover to take affect to switch to another node. What happens during this time? I think it will time out/unable to connect. BUT is there a way for it to place the request in some pipeline so when the cluster node is back up/switched over it will continue as normal? as you can see, I know nothing much about clustering! what about your own custom .NET apps? Would there be a special way to develop them? I know that you can say create a simple Hello world app, and cluster that but they wouldnt be something you could see interms of the UI or anything, so they would effectively need to be developed as a Windows Service perhaps or even as a standard Console app which runs and not wait for user input but you wouldnt see any output from it (unless you redirect output to somewhere else) What im getting at here is... for those who have experience or developed a cluster application in .NET, how did you do it and what are the things to be aware of? For example we have the cloud service - fundamentally its built on clustering - if there is an outage, another node takes place and service is resumed as normal but we dont really see much of that downtime.

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• What is the benefit of writing to a temp location, And then copying it to the intended destination?

  - by Devdatta Tengshe

  I am writing an application that works with satellite Images, and my boss asked me to look at some of the commercial application, and see how they behave. I found a strange behavior and then as I was looking, I found it in other standard applications as well. These Programs first write to the temp folder, and then copy it to the intended destination. Example: 7zip first extracts to the temp folder, and then copies the extracted data to the location that you had asked it to extract the data to. I see several problems with this approach: 1.The temp folder might not have enough space, while the intended location might have that much space. 2.If it is a large file, it can take a non-negligible amount of time for the copy operation. I thought about it a lot, but I couldn't see one single positive point to doing this. Am I missing something, or is there a real benefit to doing this?

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• .aspx websites: Is it built using web forms?

  - by Lazeera

  I visit many website which I think is built using ASP.NET web forms because of the extension (.aspx). When I view source of these website I see at least one or two something like: <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE"> or wvcD4NCjxwPtin2YTZh9iv2YrYqSDYp9mE2KvYp9mG2YrYqSDZh9mKINit2..... However, yesterday I visited two sites on is the 'ASP.NET forums - http://forums.asp.net' and the other is 'POF'. The extension of these sites is still (.aspx) but when I view the source of these site I could not find any <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE"> nor wvcD4NCjxwPtin2YTZh9iv2YrYqSDYp9mE2KvYp9mG2YrYqSDZh9mKINit2..... Now, I would like to know how those sites use ASP.NET Web Forms and their final HTML output is still clean?

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• Detect duplicate in a subset from a set of elements

  - by Abhinav Shrivastava

  I have a set of numbers say : 1 1 2 8 5 6 6 7 8 8 4 2... I want to detect the duplicate element in subsets(of given size say k) of the above numbers... For example : Consider the increasing subsets(for example consider k=3) Subset 1 :{1,1,2} Subset 2 :{1,2,8} Subset 3 :{2,8,5} Subset 4 :{8,5,6} Subset 5 :{5,6,6} Subset 6 :{6,6,7} .... .... So my algorithm should detect that subset 1,5,6 contains duplicates.. My approach : 1)Copy the 1st k elements to a temporary array(vector) 2) using #include file in C++ STL...using unique() I would determine if there's any change in size of vector.. Any other clue how to approach this problem..

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• Naming conventions used for variables and functions in C

  - by Zel

  While coding a large project in C I came upon a problem. If I keep on writing more code then there will be a time when it will be difficult for me to organize the code. I mean that the naming for functions and variables for different parts of the program may seem to be mixed up. So I was thinking whether there are useful naming conventions that I can use for C variables and functions? Most languages suggest a naming convention. But for C the only thing I have read so far is the names should be descriptive for code readability. EDIT: Examples of some examples of suggested naming conventions: Python's PEP 8 Java Tutorial I read some more naming conventions for java somewhere but couldn't remember where.

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• Search network device from LAN through my C++ application and change the IP address

  - by Arun Kumar K S

  I am developing an application in C++ to communicate with my network device. I used UDP classes to search the device from the network. I done the code in such a way that from my application a broadcast message will send to the local network. The device will respond to the broadcast message and the application will get the IP address from that response. After establishing a network communication send a message to the device for changing the IP address. That worked fine if my devices IP address is correct. But when I set a wrong IP address and subnet to the device. My application will never get any messages from the device. So I can't able communicate to the device and not able get the device and unable to change the IP address etc. Say example IP address of the device 20.1.1.1 Subnet Mask 255.0.0.0 And in my system that runs the application IP address 192.168.1.23 Subnet Mask 255.255.255.0 I tried the Lantronix device installation software with their Lantronix device in network. It listed the device from the network and I am able to change the IP address from their software. Any one know how this is done in this type of software? How I can search in network to find the device and change the IP address when its IP address is not in range? Which protocol they used to find the device?

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• How to deal with or survive with the information overload

  - by Name

  I will better explain my question. I have been struggling with this for long time Everytime i want to read something for e,g book on java , then i find so much stuff like many tutorials , many ebooks that i am not able to decide which one to choose. I spend some time reading one , then 2 and so on and in the end i leave and gain nothing. I like the old days when we had only few resources like one hard book and at least i finish that from start to finish and gained much but now days there is so much information that mind jumps from one source to other and gain nothing what should i do

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• How do I write code that doesn't suck? [closed]

  - by Afnan

  My friends and I would like to write a C# desktop application, and would like some guidance on how to make sure the code base is professional and well-kept. Should we use classes or interfaces for our inheritance patterns (which is better)? What are the best practices for professional applications? How do we know what sloppy code looks like, and how do we avoid creating sloppy code? Are there any best practices regarding the design of Winforms applications?

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• Can you point me to a nontrivial strategy pattern implementation?

  - by Eugen Martynov

  We are faced implementing a registration workflow with many branches. There are three main flows which in some conditions lead to one another. Each flow has at least four different steps; some steps interact with the server, and every step adds more information to the state. Also the requirement is to have it persistent between sessions, so if the user closes the app (this is a mobile app), it will restore the process from the last completed step with the state from the previous session. I think this could benefit from the use of the strategy pattern, but I've never had to implement it for such a complex case. Does anyone know of any examples in open source or articles from which I could find inspiration? Preferably the examples would be from a live/working/stable application. I'm interested in Java implementation mostly; we are developing for Java mobile phones: android, blackberry and J2ME. We have an SDK which is quite well separated from platform specific implementations, but examples in C++, C#, Objective-C or Python would be acceptable.

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• What language yields most rapid development of a SOAP client application

  - by mathematician1975

  I have written a SOAP client application. It started off as Perl but I needed it to have proper multithreaded capabilities, so I rewrote it in C++ which was a horrendous experience and the development time was many many times more than that of the Perl bot. I need to implement a new SOAP client and I was wondering what peoples opinions were about choice of language with regards to fastest development time. C++ is clearly not well suited to web services type programming so there is no way I am going to write in C++ again.

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• Sprite Sheets in PyGame?

  - by Eamonn

  So, I've been doing some googling, and haven't found a good solution to my problem. My problem is that I'm using PyGame, and I want to use a Sprite Sheet for my player. This is all well and good, and it would be too, if I wasn't using a Sprite Sheet strip. Basically, if you don't understand, I have a strip of 32x32 'frames'. These frames are all in an image, along side each other. So, I have 3 frames in 1 image. I'd like to be able to use them as my sprite sheet, and not have to crop them up. I have used an awesome, popular and easy-to-use game framework for Lua called LÖVE. LÖVE has these things called "Quads". They are similar to texture regions in LibGDX, if you know what they are. Basically, quads allow you to get parts of an image. You define how large a quad is, and you define parts of an image that way, or 'regions' of an image. I would like to do something similar to this in PyGame, and use a "for" loop to go through the entire image width and height and mark each 32x32 area (or whatever the user defines as their desired frame width and height) and store that in a list or something for use later on. I'd define an animation speed and stuff, but that's for later on. I've been looking around on the web, and I can't find anything that will do this. I found 1 script on the PyGame website, but it crashed PyGame when I tried to run it. I tried for hours trying to fix it, but no luck. So, is there a way to do this? Is there a way to get regions of an image? Am I going about this the wrong way? Is there a simpler way to do this? Thanks! :-)

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• How does the "Fourth Dimension" work with arrays?

  - by Questionmark

  Abstract: So, as I understand it (although I have a very limited understanding), there are three dimensions that we (usually) work with physically: The 1st would be represented by a line. The 2nd would be represented by a square. The 3rd would be represented by a cube. Simple enough until we get to the 4th -- It is kinda hard to draw in a 3D space, if you know what I mean... Some people say that it has something to do with time. The Question: Now, that is all great with me. My question isn't about this, or I'd be asking it on MathSO or PhysicsSO. My question is: How does the computer handle this with arrays? I know that you can create 4D, 5D, 6D, etc... arrays in many different programming languages, but I want to know how that works.

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• Which is the most practical way to add functionality to this piece of code?

  - by Adam Arold

  I'm writing an open source library which handles hexagonal grids. It mainly revolves around the HexagonalGrid and the Hexagon class. There is a HexagonalGridBuilder class which builds the grid which contains Hexagon objects. What I'm trying to achieve is to enable the user to add arbitrary data to each Hexagon. The interface looks like this: public interface Hexagon extends Serializable { // ... other methods not important in this context <T> void setSatelliteData(T data); <T> T getSatelliteData(); } So far so good. I'm writing another class however named HexagonalGridCalculator which adds some fancy pieces of computation to the library like calculating the shortest path between two Hexagons or calculating the line of sight around a Hexagon. My problem is that for those I need the user to supply some data for the Hexagon objects like the cost of passing through a Hexagon, or a boolean flag indicating whether the object is transparent/passable or not. My question is how should I implement this? My first idea was to write an interface like this: public interface HexagonData { void setTransparent(boolean isTransparent); void setPassable(boolean isPassable); void setPassageCost(int cost); } and make the user implement it but then it came to my mind that if I add any other functionality later all code will break for those who are using the old interface. So my next idea is to add annotations like @PassageCost, @IsTransparent and @IsPassable which can be added to fields and when I'm doing the computation I can look for the annotations in the satelliteData supplied by the user. This looks flexible enough if I take into account the possibility of later changes but it uses reflection. I have no benchmark of the costs of using annotations so I'm a bit in the dark here. I think that in 90-95% of the cases the efficiency is not important since most users wont't use a grid where this is significant but I can imagine someone trying to create a grid with a size of 5.000.000.000 X 5.000.000.000. So which path should I start walking on? Or are there some better alternatives? Note: These ideas are not implemented yet so I did not pay too much attention to good names.

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• Date calculation algorithm

  - by Julian Cuevas

  I'm working on a project to schedule a machine shop, basically I've got everything covered BUT date calculations, I've got a method called schedule (working on PHP here): public function schedule($start_date, $duration_in_minutes) Now my problem is, currently I'm calculating end time manually because time calculations have the following rules: During weekdays, work with business hours (7:00 AM to 5:00 PM) Work on Saturdays from 7:00 AM to 2:00 PM Ignore holidays (in Colombia we have A LOT of holidays) I already have a lookup table for holidays, I also have a Java version of this algorithm that I wrote for a previous version of the project, but that one's also manual. Is there any way to calculate an end time from a start time given duration?, my problem is that I have to consider the above rules, I'm looking for a (maybe?) math based solution, however I currently don't have the mind to devise such a solution myself. I'll be happy to provide code samples if necessary.

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• How does one handle sensitive data when using Github and Heroku?

  - by Jonas

  I am not yet accustomed with the way Git works (And wonder if someone besides Linus is ;)). If you use Heroku to host you application, you need to have your code checked in a Git repo. If you work on an open-source project, you are more likely going to share this repo on Github or other Git hosts. Some things should not be checked in the public repo; database passwords, API keys, certificates, etc... But these things still need to be part of the Git repo since you use it to push your code to Heroku. How to work with this use case? Note: I know that Heroku or PHPFog can use server variables to circumvent this problem. My question is more about how to "hide" parts of the code.

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• Updating an Entity through a Service

  - by GeorgeK

  I'm separating my software into three main layers (maybe tiers would be a better term): Presentation ('Views') Business logic ('Services' and 'Repositories') Data access ('Entities' (e.g. ActiveRecords)) What do I have now? In Presentation, I use read-only access to Entities, returned from Repositories or Services, to display data. $banks = $banksRegistryService->getBanksRepository()->getBanksByCity( $city ); $banksViewModel = new PaginatedList( $banks ); // some way to display banks; // example, not real code I find this approach quite efficient in terms of performance and code maintanability and still safe as long as all write operations (create, update, delete) are preformed through a Service: namespace Service\BankRegistry; use Service\AbstractDatabaseService; use Service\IBankRegistryService; use Model\BankRegistry\Bank; class Service extends AbstractDatabaseService implements IBankRegistryService { /** * Registers a new Bank * * @param string $name Bank's name * @param string $bik Bank's Identification Code * @param string $correspondent_account Bank's correspondent account * * @return Bank */ public function registerBank( $name, $bik, $correspondent_account ) { $bank = new Bank(); $bank -> setName( $name ) -> setBik( $bik ) -> setCorrespondentAccount( $correspondent_account ); if( null === $this->getBanksRepository()->getDefaultBank() ) $this->setDefaultBank( $bank ); $this->getEntityManager()->persist( $bank ); return $bank; } /** * Makes the $bank system's default bank * * @param Bank $bank * @return IBankRegistryService */ public function setDefaultBank( Bank $bank ) { $default_bank = $this->getBanksRepository()->getDefaultBank(); if( null !== $default_bank ) $default_bank->setDefault( false ); $bank->setDefault( true ); return $this; } } Where am I stuck? I'm struggling about how to update certain fields in Bank Entity. Bad solution #1: Making a series of setters in Service for each setter in Bank; - seems to be quite reduntant, increases Service interface complexity and proportionally decreases it's simplicity - something to avoid if you care about code maitainability. I try to follow KISS and DRY principles. Bad solution #2: Modifying Bank directly through it's native setters; - really bad. If you'll ever need to move modification into the Service, it will be pain. Business logic should remain in Business logic layer. Plus, there are plans on logging all of the actions and maybe even involve user permissions (perhaps, through decorators) in future, so all modifications should be made only through the Service. Possible good solution: Creating an updateBank( Bank $bank, $array_of_fields_to_update) method; - makes the interface as simple as possible, but there is a problem: one should not try to manually set isDefault flag on a Bank, this operation should be performed through setDefaultBank method. It gets even worse when you have relations that you don't want to be directly modified. Of course, you can just limit the fields that can be modified by this method, but how do you tell method's user what they can and cannot modify? Exceptions?

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• How to organise projects with dependencies on BitBucket?

  - by Timwi

  Both Mercurial and BitBucket make one fundamental assumption: 1 repo = 1 project. If I have a project that has a dependency (a library) which is shared by many projects, this assumption gets in the way. Now it is no longer possible to have a separate BitBucket page for each project while still being able to commit atomic revisions to multiple projects. If I put all the projects into one repo, they all become one “project” on BitBucket. If I put them in separate repos, it is no longer possible to know which version of the library project was in use at revision X of a dependent project. How is this situation normally solved on BitBucket, or is there explicitly no support for this common scenario?

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• Information Spilling Across Object Boundaries

  - by Winston Ewert

  Many times my business objects tend to have situations where information needs to cross object boundaries too often. When doing OO, we want information to be in one object and as much as possible all code dealing with that information should be in that object. However, business rules do not follow this principle giving me trouble. As an example suppose that we have an Order which has a number of OrderItems which refers to an InventoryItem which has a price. I invoke Order.GetTotal() which sums the result of OrderItem.GetPrice() which multiples a quantity by InventoryItem.GetPrice(). So far so good. But then we find out that some items are sold with a two for one deal. We can handle this by having OrderItem.GetPrice() do something like InventoryItem.GetPrice( quantity ) and letting InventoryItem deal with this. However, then we find out that the two-for-one deal only lasts for a particular time period. This time period needs to be based on the date of the order. Now we change OrderItem.GetPrice() to be InventoryItem.GetPrice( quatity, order.GetDate() ) But then we need to support different prices depending on how long the customer has been in the system: InventoryItem.GetPrice( quantity, order.GetDate(), order.GetCustomer() ) But then it turns out that the two-for-one deals apply not just to buying multiple of the same inventory item but multiple for any item in a InventoryCategory. At this point we throw up our hands and just give the InventoryItem the order item and allow it to travel over the object reference graph via accessors to get the information its needs: InventoryItem.GetPrice( this ) TL;DR I want to have coupling in objects, but business rules often force me to access information from all over the place in order to make particular decisions. Are there good techniques for dealing with this? Do others find the same problem?

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• Do you use your personal laptop for work?

  - by davekaro

  We're trying to get our company to let us use our own personal laptop for client work. We've agreed that any code/data will be encrypted using something like TrueCrypt, in case the laptop is stolen or lost. However, the company is still skeptical and not sure they want to allow us to use our personal machines for development. They would rather buy us laptops... but we want to use MacBook Pros and they don't want to pay for them. Even if they did buy us laptops, we would stil have the issue of needing to encrypt the code/data in case of theft/loss. Do you use your own laptop for work? What are the arguments for/against this?

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• Software design methods for Java or any other programming language

  - by IkerB

  I'm junior programmer and I would like to know how professionals write their code or which steps they follow when they are creating new software. I mean, which steps they follow, which programming methodology, software architecture design application software, etc. I would like to find a tutorial where they explain from the beginning which steps I have to follow from The Idea I have in my mind to the final version of the application in any language. Or perhaps how is your programming steps or rules that you used to follow. Because everytime I want to create the an application I spend few time on the design and a lot of time coding (I know, that's not good).

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• Why isn't reflection on the SCJP / OCJP?

  - by Nick Rosencrantz

  I read through Kathy Sierra's SCJP study guide and I will read it again more throughly to improve myself as a Java programmer and be able to take the certification either Java 6 or wait for the Java 7 exam (I'm already employed as Java developer so I'm in no hurry to take the exam.) Now I wonder why reflection is not on the exam? The book it seems covers everything that should be on the exam and AFAIK reflection is at least as important as threads if not more used inpractice since many frameworks use reflection. Do you know why reflection is not part of the SCJP? Do you agree that it's at least important to know reflection as threads? Thanks for any answer

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• How to detect if an app was already installed before

  - by Dante

  How do software applications keep track of whether the user already installed the application before in it's Windows system? Say you install app X, trial version, remove it, then re install it, and when you run it again it detects you had already installed it before. If you uninstall and clean all registry information it shouldn't know you had already installed it before... Disclaimer: I'm not trying to "hack" any application, just thinking about how this is implemented.

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• Restrictive routing best practices for Google App Engine with python?

  - by Aleksandr Makov

  Say I have a simple structure: app = webapp2.WSGIApplication([ (r'/', 'pages.login'), (r'/profile', 'pages.profile'), (r'/dashboard', 'pages.dash'), ], debug=True) Basically all pages require authentication except for the login. If visitor tries to reach a restrictive page and he isn't authorized (or lacks privileges) then he gets redirected to the login view. The question is about the routing design. Should I check the auth and ACL privs in each of the modules (pages.profile and pages.dash from example above), or just pass all requests through the single routing mechanism: app = webapp2.WSGIApplication([ (r'/', 'pages.login'), (r'/.+', 'router') ], debug=True) I'm still quite new to the GAE, but my app requires authentication as well as ACL. I'm aware that there's login directive on the server config level, but I don't know how it works and how I can tight it with my ACL logic and what's worse I cannot estimate time needed to get it running. Besides, it looks only to provide only 2 user groups: admin and user. In any case, that's the configuration I use: handlers: - url: /favicon.ico static_files: static/favicon.ico upload: static/favicon.ico - url: /static/* static_dir: static - url: .* script: main.app secure: always Or I miss something here and ACL can be set in the config file? Thanks.

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• Why is using C++ libraries is so complicated?

  - by Pius

  First of all, I want to note I love C++ and I'm one of those people who thinks it is easier to code in C++ than Java. Except for one tiny thing: libraries. In Java you can simply add some jar to the build path and you're done. In C++ you usually have to set multiple paths for the header files and the library itself. In some cases, you even have to use special build flags. I have mainly used Visual Studio, Code Blocks and no IDE at all. All 3 options do not differ much when talking about using external libraries. I wonder why was there made no simpler alternative for this? Like having a special .zip file that has everything you need in one place so the IDE can do all the work for you setting up the build flags. Is there any technical barrier for this?

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• Discuss: PLs are characterised by which (iso)morphisms are implemented

  - by Yttrill

  I am interested to hear discussion of the proposition summarised in the title. As we know programming language constructions admit a vast number of isomorphisms. In some languages in some places in the translation process some of these isomorphisms are implemented, whilst others require code to be written to implement them. For example, in my language Felix, the isomorphism between a type T and a tuple of one element of type T is implemented, meaning the two types are indistinguishable (identical). Similarly, a tuple of N values of the same type is not merely isomorphic to an array, it is an array: the isomorphism is implemented by the compiler. Many other isomorphisms are not implemented for example there is an isomorphism expressed by the following client code: match v with | ((?x,?y),?z = x,(y,z) // Felix match v with | (x,y), - x,(y,z) (* Ocaml *) As another example, a type constructor C of int in Felix may be used directly as a function, whilst in Ocaml you must write a wrapper: let c x = C x Another isomorphism Felix implements is the elimination of unit values, including those in tuples: Felix can do this because (most) polymorphic values are monomorphised which can be done because it is a whole program analyser, Ocaml, for example, cannot do this easily because it supports separate compilation. For the same reason Felix performs type-class dispatch at compile time whilst Haskell passes around dictionaries. There are some quite surprising issues here. For example an array is just a tuple, and tuples can be indexed at run time using a match and returning a value of a corresponding sum type. Indeed, to be correct the index used is in fact a case of unit sum with N summands, rather than an integer. Yet, in a real implementation, if the tuple is an array the index is replaced by an integer with a range check, and the result type is replaced by the common argument type of all the constructors: two isomorphisms are involved here, but they're implemented partly in the compiler translation and partly at run time.

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