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  • Liskov substitution and abstract classes / strategy pattern

    - by Kolyunya
    I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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  • .NET Libraries Cost More Than Windows?

    - by Kevin Mark
    When looking into libraries to make my programming life a little bit easier I've (almost) always been disappointed by the prices offered. For instance, Actipro's WPF Studio is $650. I suppose that's worth it if you plan to make money from the use of those controls. But take a look at, say, Windows. Windows 7 Ultimate is just about $220. I consider Windows to be a far more complex and "worth-it" product/purchase than a library that runs on it. Why the significant difference in pricing? Do libraries really need to be so expensive, or do they need to charge more in order to make a decent some of money?

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  • TBXML parsing issue while the value cannot get in UILabel

    - by Dany
    In my app I'm using TBXML parser where I need to get a value from xml file and print it on the label. This is my xml file in server <gold> <price> <title>22 K Gold</title> </price> <price> <title>24 K Gold</title> </price> </gold> any my Viewcontroller.h looks like #import <UIKit/UIKit.h> #import "TBXML.h" @interface ViewController : UIViewController{ IBOutlet UILabel *lab; IBOutlet UILabel *lab1; TBXML *tbxml; } @end and my Viewcontrooler.m looks like - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. NSData *xmlData = [[NSData alloc]initWithContentsOfURL:[NSURL URLWithString:@"http://www.abcde.com/sample.xml"]]; tbxml = [[TBXML alloc]initWithXMLData:xmlData]; TBXMLElement * root = tbxml.rootXMLElement; if (root) { TBXMLElement * elem_PLANT = [TBXML childElementNamed:@"price" parentElement:root]; while (elem_PLANT !=nil) { TBXMLElement * elem_BOTANICAL = [TBXML childElementNamed:@"title" parentElement:elem_PLANT]; NSString *botanicalName = [TBXML textForElement:elem_BOTANICAL]; lab.text=[NSString stringWithFormat:@"re %@", botanicalName]; elem_PLANT = [TBXML nextSiblingNamed:@"price" searchFromElement:elem_PLANT]; elem_BOTANICAL = [TBXML childElementNamed:@"title" parentElement:elem_PLANT]; botanicalName = [TBXML textForElement:elem_BOTANICAL]; lab1.text=[NSString stringWithFormat:@"re %@", botanicalName]; } } } I'm getting BAD_ACCESS thread. Am I missing anything?

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  • Why not have a High Level Language based OS? Are Low Level Languages more efficient?

    - by rtindru
    Without being presumptuous, I would like you to consider the possibility of this. Most OS today are based on pretty low level languages (mainly C/C++) Even the new ones such as Android uses JNI & underlying implementation is in C In fact, (this is a personal observation) many programs written in C run a lot faster than their high level counterparts (eg: Transmission (a bittorrent client on Ubuntu) is a whole lot faster than Vuze(Java) or Deluge(Python)). Even python compilers are written in C, although PyPy is an exception. So is there a particular reason for this? Why is it that all our so called "High Level Languages" with the great "OOP" concepts can't be used in making a solid OS? So I have 2 questions basically. Why are applications written in low level languages more efficient than their HLL counterparts? Do low level languages perform better for the simple reason that they are low level and are translated to machine code easier? Why do we not have a full fledged OS based entirely on a High Level Language?

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  • How to write a product definition?

    - by Skarab
    I would like to learn how to write a software product definition. Therefore I am looking for online materials or books, which would help me to learn more about this topic. I would like to learn: what must be in what must not to be in how to make a product definition to sell internally the product finding balance between use case descriptions (the why), and feature descriptions (the how). ... I am aware that it is not something that can learn in 15 minutes but I think such a discussion could help me to have a good start.

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  • How to hire support people?

    - by Martin
    I manage a tech support team at a mid-sized software company. We are the last line of support, so issues that we can't fix need to be escalated to the development team. When I joined the company, our team wasn't capable of much beyond using a specific set of troubleshooting steps to solve known issues and escalating anything else to the developers. It's always been a goal of mine for our team to shoulder as much of the support burden as possible without ever bothering a developer. Over the past few years, I, along with several new hires I've made, have made pretty good progress in that direction. We've coded our own troubleshooting tools which now ship with several of our products. When users have never-before-seen issues, we analyze stack traces and troubleshoot down to the code level, and if we need to submit a bug, half the time we've already identified in the code where in the code the bug is and offered a patch to fix it. Here's the problem I've always had: finding support people capable of the work I've described above is really difficult. I've hired 3 people in the past 3 years, and I've probably looked at several thousand resumes and conducted several hundred phone screens to do so. I know it's pretty well accepted that hiring good people is tough in the tech industry, but it seems that support is especially difficult -- there are clearly thousands of people walking around calling themselves support analysts, but 99%+ of them seemingly aren't capable of anything beyond reading a script. I'm curious if anyone has experience recruiting the sort of folks I'm talking about, and if you have any suggestions to share. We've tried all sorts of things -- different job titles/descriptions, using headhunters, etc. And while we've managed to hire a few good folks, it's basically taken us a year to find an appropriate candidate for each opening we've had, and I can't help but wonder if there's something we could be doing differently.

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  • Is big (as much as big) size display (Monitor) always better for Development?

    - by Jitendra Vyas
    Is bigger size display ( Monitor) always better for Development? I'm going to buy a new LCD Monitor. I mostly work in Adobe Photoshop, HTML, CSS, jQuery and Wordpress. Budget is not a problem. Many options are there for LCD Monitor SIZE My questions are Would it better for maximum size, or large size monitor are not good always? Would it better to buy 21.5 inch x 2 than one 30 inch monitor? Which monitor size would you would prefer between the size of 21.5 inch - 30 inch, if bugdet is not a problem?

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  • Is this the right strategy to convert an in-level order binary tree to a doubly linked list?

    - by Ankit Soni
    So I recently came across this question - Make a function that converts a in-level-order binary tree into a doubly linked list. Apparently, it's a common interview question. This is the strategy I had - Simply do a pre-order traversal of the tree, and instead of returning a node, return a list of nodes, in the order in which you traverse them. i.e return a list, and append the current node to the list at each point. For the base case, return the node itself when you are at a leaf. so you would say left = recursive_function(node.left) right = recursive_function(node.right) return(left.append(node.data)).append(right);` Is this the right approach?

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  • Seeking solution for printing-reporting .NET

    - by Parhs
    I am developing an application that prints in separate threads in extreme cases about 20-25 pages per minute to various thermal printers. Currently templates for these are XAML xps documents. All printers have graphics drivers that support EMF/GDI printing. So GDI-EMF is done by operating system resulting in slower performance. Sending raw text for printing is another good solution but doesnt work always , because some clients have old chinese thermal printer that nobody support thus impossible to change codepage / emulation. So it doesnt work always. Also most computers running my software are low end ATOM CPU. So I am thinking to return to GDI, EMF printing and have both Text-Only reports and EMF reports. Another reason i want EMF is because here receipts are signed by Electronic Fiscal Memory device.Most of these dont do good job extracting text from XPS as they dont follow the standard but how windows convert GDI to XPS.Even with text-only mode some of them dont support all character encodings and are impossible to send paper cut command after the sign. I know that using a reporting engine would solve rendering problem but I dont want to buy one. All I want is to be able to show tabular data and insert an image and replaced text.I know there is StringTemplate that could do the generation of template but the problem is i should parse somehow the template and render it using GDI commands. Is there any other solution/approach for this ? Or is there anything ready ?

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  • Finding the order of a set's elements

    - by Maciej Stachowski
    A little rephrased, in the form of a game, real-life problem: Suppose there is a set of elements {1, 2, ..., n}. Player A has chosen a single permutation of this set. Player B wants to find out the order of the elements by asking questions of form "Is X earlier in the permutation than Y?", where X and Y are elements of the set. Assuming B wants to minimize the amount of questions, how many times would he have to ask, and what would be the algorithm?

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  • Configurable tables in sql database

    - by dot
    I have the following tables in my database: Config Table: ====================================== Start_Range | End Range | Config_id 10 | 15 | 1 ====================================== Available_UserIDs ========================== ID | UserID | Used_YN | 1 | 10 | t | 1 | 11 | f | 1 | 12 | f | 1 | 13 | f | 1 | 14 | f | 1 | 15 | f | ========================== Users ========================== UserId | FName | LName | 10 |John | Doe | ========================== This is used in a reservation system of sorts... which lets an administrator specify a range of numbers that will be assigned to users in the config table. Once the range has been defined, the system then populates the Available_userIDs table with all the numbers in between the range, and sets the Used_YN flag to false As users sign up, they grab the next user_id number that's not in use... and reserve it. Then the system adds a record to the Users table. Once the admin has specified a range, it is possible that they can change it. For example, they can start with 10-15... and then when the range is used up, they should be able to specify another range like 16 - 99. I've put a unique constraint on the Available_UserIDs table, as well as on the Users table - to ensure that UserIds can't be duplicated. My questions are as follows: What's the best way to prevent the admins from using a range that's already in use? I thought of the following options: -- check either the Users table to see if the start range or ending range numbers are being used. If they are, assume that all the numbers in between are in use too, and reject the range. -- let them specify whatever they want, try to populate the Available_UserIDs table. If there are duplicates, just ignore that specific error message from the database and continue on. How do I find gaps in the number ranges? For example, if they specify 10-15, and then 20-25, it'd be nice to be able to somehow suggest on my web page that 16-19 is currently available. I found this article: http://stackoverflow.com/questions/1312101/how-to-find-a-gap-in-running-counter-with-sql But it only seems to return the first available number... so in my example above, it would only return the number 16. I'm sure there's a simpler way to do things that I'm overlooking!

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  • Better solution then simple factory method when concrete implementations have different attributes

    - by danip
    abstract class Animal { function eat() {..} function sleep() {..} function isSmart() } class Dog extends Animal { public $blnCanBark; function isSmart() { return $this->blnCanBark; } } class Cat extends Animal { public $blnCanJumpHigh; function isSmart() { return $this->blnCanJumpHigh; } } .. and so on up to 10-20 animals. Now I created a factory using simple factory method and try to create instances like this: class AnimalFactory { public static function create($strName) { switch($strName) { case 'Dog': return new Dog(); case 'Cat': return new Cat(); default: break; } } } The problem is I can't set the specific attributes like blnCanBark, blnCanJumpHigh in an efficient way. I can send all of them as extra params to create but this will not scale to more then a few classes. Also I can't break the inheritance because a lot of the basic functionality is the same. Is there a better pattern to solve this?

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  • What tools are available for remote communication when working from home or with a distributed team?

    - by Ryan Hayes
    My supervisor is allowing my team to dip our toes in the water of working from home. Considering a recent aquisition of another company is requiring some employees to love this new idea which will hack up to an hour off their commute into work every morning, I really want this to succeed. In order to make it a success, we need good tools to make our lives a lot easier. We currently are set up with OpenVPN, and Team Foundation Server 2010 with SharePoint 2010, and use Live Messenger (for SharePoint integration and easier remote desktop) for IM. These are just what we use (and they are currently working well) , but you can suggest other products. So, what are some great tools that will helps us collaborate, communicate, and generally work together when we're hours apart?

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  • Would adding award points or game features to workplace software be viewed poorly amongst the programming community?

    - by Eric P
    So one of my responsibilities at work is to build an internal tool that helps the workers enter in all their information. It's an enterprise application that is similar to a Windows forms database tool. So it's not much different than like developing a Word + Excel combo application, but the average person in this workgroup is a 20-40 year old woman or a random chatty male type. Plus I know all of these people are heavily involved with Facebook on a daily basis. How bad would it be if I styled my new interface to be similar to what Facebook does. People could get award points and stuff when they fill out different types of forms and basically compete against each other like it was a game. When people had completed one, it would be posted on their wall and everyone could comment/like stuff just like in Facebook. And it would be like they are doing peer reviewing for fun. The rewards would be outstanding I would imagine. These people are so into Facebook and Facebook games that productivity would rise due to them trying to compete and earn points and achievements. Would this be taking advantage of the people by 'tricking them into working harder by giving them a game' or would it be viewed as something that would improve happiness at work?

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  • Intel programming "performance" books? [closed]

    - by user997112
    I vaguely remember seeing that Intel have produced a few good books, especially with regards to low latency programming, but I cannot remember the titles. Could people suggest the titles of Intel books (or ones relating to Intel products)? Examples include books on: -Intel Compiler -Intel Assembler -Any low level programming on Intel assembler -The Intel CPU architecture -Intel threading blocks library

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  • Which programming language do you think is the most beautiful and which the ugliest? [closed]

    - by user1598390
    I would like to hear opinions about what programming language do you consider to produce the most legible, self-documenting, intention-transparent, beautiful-looking code ? And which produces the most messy-looking, unintentionally obfuscated, ugly code, regardless of it being good code ? Let me clarify: I'm talking about the syntax, "noise vs signal", structure of the language. Assignment operators. De-referencing. Whether it's dot syntax or "-" syntax. What languages do you think are inherently harder to read than others, given all other things being equal like, say, code quality, absence of code smells, etc. ?

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  • Customizing the NUnit GUI for data-driven testing

    - by rwong
    My test project consists of a set of input data files which is fed into a piece of legacy third-party software. Since the input data files for this software are difficult to construct (not something that can be done intentionally), I am not going to add new input data files. Each input data file will be subject to a set of "test functions". Some of the test functions can be invoked independently. Other test functions represent the stages of a sequential operation - if an earlier stage fails, the subsequent stages do not need to be executed. I have experimented with the NUnit parametrized test case (TestCaseAttribute and TestCaseSourceAttribute), passing in the list of data files as test cases. I am generally satisfied with the the ability to select the input data for testing. However, I would like to see if it is possible to customize its GUI's tree structure, so that the "test functions" become the children of the "input data". For example: File #1 CheckFileTypeTest GetFileTopLevelStructureTest CompleteProcessTest StageOneTest StageTwoTest StageThreeTest File #2 CheckFileTypeTest GetFileTopLevelStructureTest CompleteProcessTest StageOneTest StageTwoTest StageThreeTest This will be useful for identifying the stage that failed during the processing of a particular input file. Is there any tips and tricks that will enable the new tree layout? Do I need to customize NUnit to get this layout?

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  • Isolated Unit Tests and Fine Grained Failures

    - by Winston Ewert
    One of the reasons often given to write unit tests which mock out all dependencies and are thus completely isolated is to ensure that when a bug exists, only the unit tests for that bug will fail. (Obviously, an integration tests may fail as well). That way you can readily determine where the bug is. But I don't understand why this is a useful property. If my code were undergoing spontaneous failures, I could see why its useful to readily identify the failure point. But if I have a failing test its either because I just wrote the test or because I just modified the code under test. In either case, I already know which unit contains a bug. What is the useful in ensuring that a test only fails due to bugs in the unit under test? I don't see how it gives me any more precision in identifying the bug than I already had.

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  • Rewriting GPL code to change license

    - by I_like_traffic_lights
    I have found a GPL library (no dual license), which does exactly what I need. Unfortunately, the GPL license on the library is incompatible with the license of a different library I use. I have therefore decided to rewrite the GPL library, so the license can be changed. My question is: How extensive do the changes need to be to the library in order to be able to change the license? In other words, what is the cheapest way to do this?

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  • "Programming error" exceptions - Is my approach sound?

    - by Medo42
    I am currently trying to improve my use of exceptions, and found the important distinction between exceptions that signify programming errors (e.g. someone passed null as argument, or called a method on an object after it was disposed) and those that signify a failure in the operation that is not the caller's fault (e.g. an I/O exception). As far as I understand, it makes little sense for an immediate caller to actually handle programming error exceptions, he should instead assure that the preconditions are met. Only "outer" exception handlers at task boundaries should catch them, so they can keep the system running if a task fails. In order to ensure that client code can cleanly catch "failure" exceptions without catching error exceptions by mistake, I create my own exception classes for all failure exceptions now, and document them in the methods that throw them. I would make them checked exceptions in Java. Now I have a few questions: Before, I tried to document all exceptions that a method could throw, but that sometimes creates an unwiedly list that needs to be documented in every method up the call chain until you can show that the error won't happen. Instead, I document the preconditions in the summary / parameter descriptions and don't even mention what happens if they are not met. The idea is that people should not try to catch these exceptions explicitly anyway, so there is no need to document their types. Would you agree that this is enough? Going further, do you think all preconditions even need to be documented for every method? For example, calling methods in IDisposable objects after calling Dispose is an error, but since IDisposable is such a widely used interface, can I just assume a programmer will know this? A similar case is with reference type parameters where passing null makes no conceivable sense: Should I document "non-null" anyway? IMO, documentation should only cover things that are not obvious, but I am not sure where "obvious" ends.

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  • To branch or not to branch?

    - by Idsa
    Till recently my development workflow was the following: Get the feature from product owner Make a branch (if feature is more than 1 day) Implement it in a branch Merge changes from main branch to my branch (to reduce conflicts during backward merging) Merge my branch back to main branch Sometimes there were problems with merging, but in general I liked it. But recently I see more and more followers of idea to not make branches as it makes more difficult to practice continuous integration, continuous delivery, etc. And it sounds especially funny from people with distributed VCS background who were talking so much about great merging implementations of Git, Mercurial, etc. So the question is should we use branches nowadays?

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  • WCF Keep Alive: Whether to disable keepAliveEnabled

    - by Lijo
    I have a WCF web service hosted in a load balanced environment. I do not need any WCF session related functionality in the service. QUESTION What are the scenarios in which performances will be best if keepAliveEnabled = false keepAliveEnabled = true Reference From Load Balancing By default, the BasicHttpBinding sends a connection HTTP header in messages with a Keep-Alive value, which enables clients to establish persistent connections to the services that support them. This configuration offers enhanced throughput because previously established connections can be reused to send subsequent messages to the same server. However, connection reuse may cause clients to become strongly associated to a specific server within the load-balanced farm, which reduces the effectiveness of round-robin load balancing. If this behavior is undesirable, HTTP Keep-Alive can be disabled on the server using the KeepAliveEnabled property with a CustomBinding or user-defined Binding.

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  • Set Covering : Runtime hang\error at function call in c

    - by EnthuCrazy
    I am implementing a set covering application which uses cover function int cover(set *skill_list,set *player_list,set *covering) Suppose skill_set={a,b,c,d,e}, player_list={s1,s2,s3} then output coverin ={s1,s3} where say s1={a,b,c}, s3={d,e} and s2={b,d}. Now when I am calling this function it's hanging at run (set_cover.exe stopped working). Here is my cover function: typedef struct Spst_{ void *key; set *st; }Spst; int cover(set *skill_list,set *player_list,set *covering) { Liste *member,*max_member; Spst *subset; set *intersection; void **data; int max_size; set_init(covering); //to initialize set covering initially while(skill_list->size>0&&player_list->size>0) { max_size=0; for(member=player_list->head;member!=NULL;member=member->next) { if(set_intersection(intersection,((Spst *)(member->data))->st,skill_list)!=0) return -1; if(intersection->size>max_size) { max_member=member; max_size=intersection->size; } set_destroy(intersection); //at the end of iteration } if(max_size==0) //to check for no covering return -1; subset=(Spst *)max_member->data; //to insert max subset from play list to covering set set_inselem(covering,subset); for(member=(((Spst *)max_member->data)->st->head);member!=NULL;member=member->next) //to rem elem from skill list { data=(void **)member->data; set_remelem(skill_list,data); } set_remelem(player_list,(void **)subset); //to rem subset from set of subsets play list } if(skill_list->size>0) return -1; return 0; } Now assuming I have defined three set type sets(as stated above) and calling from main as cover(skills,subsets,covering);=> runtime hang Here Please give inputs on the missing link in this or the prerequisites for a proper call to this function type required. EDIT: Assume other functions used in cover are tested and working fine.

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  • When does the "Do One Thing" paradigm become harmful?

    - by Petr
    For the sake of argument here's a sample function that prints contents of a given file line-by-line. Version 1: void printFile(const string & filePath) { fstream file(filePath, ios::in); string line; while (file.good()) { getline(file, line); cout << line << endl; } } I know it is recommended that functions do one thing at one level of abstraction. To me, though code above does pretty much one thing and is fairly atomic. Some books (such as Robert C. Martin's Clean Code) seem to suggest breaking the above code into separate functions. Version 2: void printLine(const string & line) { cout << line << endl; } void printLines(fstream & file) { string line; while (file.good()) { getline(file, line); printLine(line); } } void printFile(const string & filePath) { fstream file(filePath, ios::in); printLines(file); } I understand what they want to achieve (open file / read lines / print line), but isn't it a bit of overkill? The original version is simple and in some sense already does one thing - prints a file. The second version will lead to a large number of really small functions which may be far less legible than the first version. Wouldn't it be, in this case, better to have the code at one place? At which point does the "Do One Thing" paradigm become harmful?

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  • When not to use Spring to instantiate a bean?

    - by Rishabh
    I am trying to understand what would be the correct usage of Spring. Not syntactically, but in term of its purpose. If one is using Spring, then should Spring code replace all bean instantiation code? When to use or when not to use Spring, to instantiate a bean? May be the following code sample will help in you understanding my dilemma: List<ClassA> caList = new ArrayList<ClassA>(); for (String name : nameList) { ClassA ca = new ClassA(); ca.setName(name); caList.add(ca); } If I configure Spring it becomes something like: List<ClassA> caList = new ArrayList<ClassA>(); for (String name : nameList) { ClassA ca = (ClassA)SomeContext.getBean(BeanLookupConstants.CLASS_A); ca.setName(name); caList.add(ca); } I personally think using Spring here is an unnecessary overhead, because The code the simpler to read/understand. It isn't really a good place for Dependency Injection as I am not expecting that there will be multiple/varied implementation of ClassA, that I would like freedom to replace using Spring configuration at a later point in time. Am I thinking correct? If not, where am I going wrong?

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