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• Code Golf: Evaluating Mathematical Expressions

  - by Noldorin

  Challenge Here is the challenge (of my own invention, though I wouldn't be surprised if it has previously appeared elsewhere on the web). Write a function that takes a single argument that is a string representation of a simple mathematical expression and evaluates it as a floating point value. A "simple expression" may include any of the following: positive or negative decimal numbers, +, -, *, /, (, ). Expressions use (normal) infix notation. Operators should be evaluated in the order they appear, i.e. not as in BODMAS, though brackets should be correctly observed, of course. The function should return the correct result for any possible expression of this form. However, the function does not have to handle malformed expressions (i.e. ones with bad syntax). Examples of expressions: 1 + 3 / -8 = -0.5 (No BODMAS) 2*3*4*5+99 = 219 4 * (9 - 4) / (2 * 6 - 2) + 8 = 10 1 + ((123 * 3 - 69) / 100) = 4 2.45/8.5*9.27+(5*0.0023) = 2.68... Rules I anticipate some form of "cheating"/craftiness here, so please let me forewarn against it! By cheating, I refer to the use of the eval or equivalent function in dynamic languages such as JavaScript or PHP, or equally compiling and executing code on the fly. (I think my specification of "no BODMAS" has pretty much guaranteed this however.) Apart from that, there are no restrictions. I anticipate a few Regex solutions here, but it would be nice to see more than just that. Now, I'm mainly interested in a C#/.NET solution here, but any other language would be perfectly acceptable too (in particular, F# and Python for the functional/mixed approaches). I haven't yet decided whether I'm going to accept the shortest or most ingenious solution (at least for the language) as the answer, but I would welcome any form of solution in any language, except what I've just prohibited above! My Solution I've now posted my C# solution here (403 chars). Update: My new solution has beaten the old one significantly at 294 chars, with the help of a bit of lovely regex! I suspected that this will get easily beaten by some of the languages out there with lighter syntax (particularly the funcional/dynamic ones), and have been proved right, but I'd be curious if someone could beat this in C# still. Update I've seen some very crafty solutions already. Thanks to everyone who has posted one. Although I haven't tested any of them yet, I'm going to trust people and assume they at least work with all of the given examples. Just for the note, re-entrancy (i.e. thread-safety) is not a requirement for the function, though it is a bonus. Format Please post all answers in the following format for the purpose of easy comparison: Language Number of characters: ??? Fully obfuscated function: (code here) Clear/semi-obfuscated function: (code here) Any notes on the algorithm/clever shortcuts it takes.

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• What is lambda expression.

  - by stackuser1

  What is lambda expression, any tutorial or link is avilable?

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• .NET Regular expressions on bytes instead of chars

  - by brickner

  Hi, I'm trying to do some parsing that will be easier using regular expressions. The input is an array (or enumeration) of bytes. I don't want to convert the bytes to chars for the following reasons: Computation efficiency Memory consumption efficiency Some non-printable bytes might be complex to convert to chars. Not all the bytes are printable. So I can't use Regex. The only solution I know, is using Boost.Regex (which works on bytes - C chars), but this is a C++ library that wrapping using C++/CLI will take considerable work. How can I use regular expressions on bytes in .NET directly, without working with .NET strings and chars? Thank you.

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• Insert string from database into an aspx and have databinding expressions within that text evaluated

  - by Christopher Edwards

  Well, as you can see I want something quick-and-dirty! How can I get a string from a db that has aspx databinding syntax in it and have the databinding expressions evaluated? So I have text such as this stored in the DB:- Hello <%=User.Name %> I haven't seen you since <%=User.LastVisit %> And I want it to be inserted here say:- ... <body> <form id="form1" runat="server"> <div> <asp:FormView ID="FormView1" DataSourceID="DataSource1" runat="server"> <ItemTemplate> <-- insert stuff here! --> ... But with the databinding expressions evaluated. I'd rather not build a full parsing, templating and evaluation engine...

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• Add values to standard expressions list in Regular Expression Editor dialog in VS 2008

  - by Alex

  Hi. In the "Regular Expression Editor" dialog in VS 2008 ( or 2005 for this matter ) , there is a list of "standard expressions" like : "French phone number" , "French postal code" etc.. And of course there is an option to select a "Custom" and then enter your own regular expression. Well.. I want to add a predefined expressions to that list . Like : "Israeli phone number" . I don't want to enter it every time by selecting a custom value . I want my developers in the team available items for them to choose. Anyone knows how to alter that list ? I've found some question about it on the web - and the answer given is that it's not possible . But that was at 2004. Anyone ?!?! Thanks.

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• Using System.DateTime in a C# Lambda expression gives an exception

  - by Samantha J

  I tried to implement a suggestion that came up in another question: Stackoverflow question Snippet here: public static class StatusExtensions { public static IHtmlString StatusBox<TModel>( this HtmlHelper<TModel> helper, Expression<Func<TModel, RowInfo>> ex ) { var createdEx = Expression.Lambda<Func<TModel, DateTime>>( Expression.Property(ex.Body, "Created"), ex.Parameters ); var modifiedEx = Expression.Lambda<Func<TModel, DateTime>>( Expression.Property(ex.Body, "Modified"), ex.Parameters ); var a = "a" + helper.HiddenFor(createdEx) + helper.HiddenFor(modifiedEx); return new HtmlString( "Some things here ..." + helper.HiddenFor(createdEx) + helper.HiddenFor(modifiedEx) ); } } When implemented I am getting the following exception which I don't really understand. The exception points to the line starting with "var createdEx =" System.ArgumentException was unhandled by user code Message=Expression of type 'System.Nullable`1[System.DateTime]' cannot be used for return type 'System.DateTime' Source=System.Core StackTrace: Can anyone help me out and suggest what I could do to resolve the exception?

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• Summation using Lambda C# 3.0

  - by Newbie

  I have a small thing. public int GetSum(List<int> x) { foreach (int i in x) sum += i; return sum; } where x is a List of integers defined as List<int> l = new List<int>(); l.Add(4); l.Add(2); l.Add(5); l.Add(8); l.Add(6); and has been passed as GetSum(l) Is it possible to rewrite the above foreach loop using a lambda? Reason: I started looking into the lambda stuffs since yesterday and is interested to learn .. however simple it may be. Thanks.

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• php array regular expressions

  - by bell

  I am using regular expressions in php to match postcodes found in a string. The results are being returned as an array, I was wondering if there is any way to assign variables to each of the results, something like $postcode1 = first match found $postcode2 = second match found here is my code $html = "some text here bt123ab and another postcode bt112cd"; preg_match_all("/([a-zA-Z]{2})([0-9]{2,3})([a-zA-Z]{2})/", $html, $matches, PREG_SET_ORDER); foreach ($matches as $val) { echo $val[0]; } I am very new to regular expressions and php, forgive me if this is a stupid question. Thanks in advance

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• "Cannot use fixed local inside lambda expression"

  - by JulianR

  I have an XNA 3.0 project that compiled just fine in VS2008, but that gives compile errors in VS2010 (with XNA 4.0 CTP). The error: Cannot use fixed local 'depthPtr' inside an anonymous method, lambda expression, or query expression depthPtr is a fixed float* into an array, that is used inside a Parallel.For lambda expression from System.Threading. As I said, this compiled and ran just fine on VS2008, but it does not on VS2010, even when targeting .NET 3.5. Has this changed in .NET 4.0, and even so, shouldn't it still compile when I choose .NET 3.5 as the target framework? Searching for the term "Cannot use fixed local" yields exactly one (useless) result, both in Google and Bing. If this has changed, what is the reason for this? I can imagine capturing a fixed pointer-type in a closure could get a bit weird, is that why? So I'm guessing this is bad practice? And before anyone asks: no, the use of pointers is not absolutely critical here. I would still like to know though :)

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• template expressions and visual studio 2005 c++

  - by chris

  I'd like to build the olb3d library with my visual studio 2005 compiler but this failes due to template errors. To be more specific, the following expression seem to be a problem: void function(T u[Lattice::d]) On the website of the project is stated that prpably my compiler is not capable of such complicated template expressions - one should use the gcc 3.4.1. My question is now if there is a way to upgrade my vs c++ compiler so it can handle template expressions on the level as the gcc 3.4.1? Maybe it helps if I get a newer version of visual studio? Cheers C.

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• Change the for loop with lambda(C#3.0)

  - by Newbie

  Is it possible to do the same using Lambda for (int i = 0; i < objEntityCode.Count; i++) { options.Attributes[i] = new EntityCodeKey(); options.Attributes[i].EntityCode = objEntityCode[i].EntityCodes; options.Attributes[i].OrganizationCode = Constants.ORGANIZATION_CODE; } I mean to say to rewrite the statement using lambda. I tried with Enumerable.Range(0,objEntityCode.Count-1).Foreach(i=> { options.Attributes[i] = new EntityCodeKey(); options.Attributes[i].EntityCode = objEntityCode[i].EntityCodes; options.Attributes[i].OrganizationCode = Constants.ORGANIZATION_CODE; }); but not working I am using C#3.0

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• Creating a property setter delegate

  - by Jim C

  I have created methods for converting a property lambda to a delegate: public static Delegate MakeGetter<T>(Expression<Func<T>> propertyLambda) { var result = Expression.Lambda(propertyLambda.Body).Compile(); return result; } public static Delegate MakeSetter<T>(Expression<Action<T>> propertyLambda) { var result = Expression.Lambda(propertyLambda.Body).Compile(); return result; } These work: Delegate getter = MakeGetter(() => SomeClass.SomeProperty); object o = getter.DynamicInvoke(); Delegate getter = MakeGetter(() => someObject.SomeProperty); object o = getter.DynamicInvoke(); but these won't compile: Delegate setter = MakeSetter(() => SomeClass.SomeProperty); setter.DynamicInvoke(new object[]{propValue}); Delegate setter = MakeSetter(() => someObject.SomeProperty); setter.DynamicInvoke(new object[]{propValue}); The MakeSetter lines fail with "The type arguments cannot be inferred from the usage. Try specifying the type arguments explicitly." Is what I'm trying to do possible? Thanks in advance.

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• IComparer using Lambda Expression

  - by josephj1989

  class p { public string Name { get; set; } public int Age { get; set; } }; static List<p> ll = new List<p> { new p{Name="Jabc",Age=53},new p{Name="Mdef",Age=20}, new p{Name="Exab",Age=45},new p{Name="G123",Age=19} }; protected static void SortList() { IComparer<p> mycomp = (x, y) => x.Name.CompareTo(y.Name); <==(Line 1) ll.Sort((x, y) => x.Name.CompareTo(y.Name));<==(Line 2) } Here the List.sort expects an IComparer<p> as a parameter. And it works with the lambda as shown in Line 2. But when I try to do as in Line 1, I get an error: Cannot convert lambda expression to type System.Collections.Generic.IComparer' because it is not a delegate type I investigated this for quite some time but I still don't understand it. Maybe my understanding of IComparer is not quite good.

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• Getting started with character and text processing (encoding, regular expressions)

  - by TK

  I'd like to learn foundations of encodings, characters and text. Understanding these is important for dealing with a large set of text whether that are log files or text source for building algorithms for collective intelligence. My current knowledge is pretty basic: something like "As long as I use UTF-8, I'm okay." I don't say I need to learn about advanced topics right away. But I need to know: Bit and bytes level knowledge of encodings. Characters and alphabets not used in English. Multi-byte encodings. (I understand some Chinese and Japanese. And parsing them is important.) Regular expressions. Algorithm for text processing. Parsing natural languages. I also need an understanding of mathematics and corpus linguistics. The current and future web (semantic, intelligent, real-time web) needs processing, parsing and analyzing large text. I'm looking for some resources (maybe books?) that get me started with some of the bullets. (I find many helpful discussion on regular expressions here on Stack Overflow. So, you don't need to suggest resources on that topic.)

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• Java remove HTML from String without regular expressions

  - by behrk2

  Hello, I am trying to remove all HTML elements from a String. Unfortunately, I cannot use regular expressions because I am developing on the Blackberry platform and regular expressions are not yet supported. Is there any other way that I can remove HTML from a string? I read somewhere that you can use a DOM Parser, but I couldn't find much on it. Text with HTML: <![CDATA[As a massive asteroid hurtles toward Earth, NASA head honcho Dan Truman (<a href="http://www.netflix.com/RoleDisplay/Billy_Bob_Thornton/20000303">Billy Bob Thornton</a>) hatches a plan to split the deadly rock in two before it annihilates the entire planet, calling on Harry Stamper (<a href="http://www.netflix.com/RoleDisplay/Bruce_Willis/99786">Bruce Willis</a>) -- the world's finest oil driller -- to head up the mission. With time rapidly running out, Stamper assembles a crack team and blasts off into space to attempt the treacherous task. <a href="http://www.netflix.com/RoleDisplay/Ben_Affleck/20000016">Ben Affleck</a> and <a href="http://www.netflix.com/RoleDisplay/Liv_Tyler/162745">Liv Tyler</a> co-star.]]> Text without HTML: As a massive asteroid hurtles toward Earth, NASA head honcho Dan Truman (Billy Bob Thornton) hatches a plan to split the deadly rock in two before it annihilates the entire planet, calling on Harry Stamper (Bruce Willis) -- the world's finest oil driller -- to head up the mission. With time rapidly running out, Stamper assembles a crack team and blasts off into space to attempt the treacherous task.Ben Affleck and Liv Tyler co-star. Thanks!

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• How to embed XBase expressions in an Xtext DSL

  - by Marcus Mathioudakis

  I am writing a simple little DSL for specifying constraints on messages, and Have been trying without success for a while to embed XBase expressions into the language. The Grammar looks like this: grammar org.xtext.businessrules.BusinessRules with org.eclipse.xtext.xbase.Xbase //import "http://www.eclipse.org/xtext/xbase/Xbase" as xbase import "http://www.eclipse.org/xtext/common/JavaVMTypes" as jvmTypes generate businessRules "http://www.xtext.org/businessrules/BusinessRules" Start: rules+=Constraint*; Constraint: {Constraint} 'FOR' 'PAYLOAD' payload=PAYLOAD 'ELEMENT' element=ID 'CONSTRAINED BY' constraint=XExpression; PAYLOAD: "SimulationSessionEvents" |"stacons" |"any" ; Range: 'above' min=INT ('below' max=INT)? |'below' max=INT ('above' min=INT)? ; When trying to parse a file such as: FOR PAYLOAD SimulationSessionEvents ELEMENT matrix CONSTRAINED BY ... I can't get it to work for ... = any kind of Arithmetic expression, although it works for ...= loop or if expression, or even just a number. As soon as I do something like '-5' or '4-5' it says Couldn't resolve reference to JvmIdentifiableElement '-', even though the Xbase.xtext Grammar looks like it allows these expressions. I don't think I'm missing any Jars, as it doesn't complain when I run the mwe workflow, but only when trying to parse the input file. Any help would be much appreciated.

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• Can this be done using LINQ/Lambda, C#3.0

  - by Newbie

  Objective: Generate dates based on Week Numbers Input: StartDate, WeekNumber Output: List of dates from the Week number specified till the StartDate i.e. If startdate is 23rd April, 2010 and the week number is 1, then the program should return the dates from 16th April, 2010 till the startddate. The function public List<DateTime> GetDates(DateTime startDate,int weeks) { List<DateTime> dt = new List<DateTime>(); int days = weeks * 7; DateTime endDate = startDate.AddDays(-days); TimeSpan ts = startDate.Subtract(endDate); for (int i = 0; i <= ts.Days; i++) { DateTime dt1 = endDate.AddDays(i); dt.Add(dt1); } return dt; } I am calling this function as DateTime StartDate = DateTime.ParseExact("20100423", "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture); List<DateTime> dtList = GetDates(StartDate, 1); The program is working fine. Question is using C# 3.0 feature like Linq, Lambda etc. can I rewrite the program. Why? Because I am learning linq and lambda and want to implement the same. But as of now the knowledge is not sufficient to do the same by myself. Thanks.

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• Square Brackets in Python Regular Expressions (re.sub)

  - by user1479984

  I'm migrating wiki pages from the FlexWiki engine to the FOSwiki engine using Python regular expressions to handle the differences between the two engines' markup languages. The FlexWiki markup and the FOSwiki markup, for reference. Most of the conversion works very well, except when I try to convert the renamed links. Both wikis support renamed links in their markup. For example, Flexwiki uses: "Link To Wikipedia":[http://www.wikipedia.org/] FOSwiki uses: [[http://www.wikipedia.org/][Link To Wikipedia]] both of which produce something that looks like I'm using the regular expression renameLink = re.compile ("\"(?P<linkName>[^\"]+)\":\[(?P<linkTarget>[^\[\]]+)\]") to parse out the link elements from the FlexWiki markup, which after running through something like "Link Name":[LinkTarget] is reliably producing groups <linkName> = Link Name <linkTarget = LinkTarget My issue occurs when I try to use re.sub to insert the parsed content into the FOSwiki markup. My experience with regular expressions isn't anything to write home about, but I'm under the impression that, given the groups <linkName> = Link Name <linkTarget = LinkTarget a line like line = renameLink.sub ( "[[\g<linkTarget>][\g<linkName>]]" , line ) should produce [[LinkTarget][Link Name]] However, in the output to the text files I'm getting [[LinkTarget [[Link Name]] which breaks the renamed links. After a little bit of fiddling I managed a workaround, where line = renameLink.sub ( "[[\g<linkTarget>][ [\g<linkName>]]" , line ) produces [[LinkTarget][ [[Link Name]] which, when displayed in FOSwiki looks like <[[Link Name> <--- Which WORKS, but isn't very pretty. I've also tried line = renameLink.sub ( "[[\g<linkTarget>]" + "[\g<linkName>]]" , line ) which is producing [[linkTarget [[linkName]] There are probably thousands of instances of these renamed links in the pages I'm trying to convert, so fixing it by hand isn't any good. For the record I've run the script under Python 2.5.4 and Python 2.7.3, and gotten the same results. Am I missing something really obvious with the syntax? Or is there an easy workaround?

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• Ambiguous call between methods ASP.NET MVC

  - by GuiPereira

  I'm pretty new in ASP.NET MVC (about 3 months) and i've the followin issue: I have a Entity Class called 'Usuario' in a ClassLibrary referenced as 'Core' and, when i create a strongly-typed view and add a html.textboxfor< like: <%= Html.TextBoxFor(u => u.Login) %> it raises the following error: Error 3 The call is ambiguous between the following methods or properties: 'Microsoft.Web.Mvc.ExpressionInputExtensions.TextBoxFor<Core.Usuario,string>(System.Web.Mvc .HtmlHelper<Core.Usuario>, System.Linq.Expressions.Expression<System.Func<Core.Usuario,string>>)' and 'System.Web.Mvc.Html.InputExtensions.TextBoxFor<Core.Usuario,string>(System.Web.Mvc.HtmlHel per<Core.Usuario>, System.Linq.Expressions.Expression<System.Func<Core.Usuario,string>>)' d:\Documents\Visual Studio 2008\Projects\GuiPereiraMVC2\GuiPereiraMVC2\Views\Gestao\Index.aspx 20 25 GuiPereiraMVC2 anyone knows why?

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• Will C++1x support __stdcall or extern "C" capture-nothing lambdas?

  - by Daniel Trebbien

  Yesterday I was thinking about whether it would be possible to use the convenience of C++1x lambda functions to write callbacks for Windows API functions. For example, what if I wanted to use a lambda as an EnumChildProc with EnumChildWindows? Something like: EnumChildWindows(hTrayWnd, CALLBACK [](HWND hWnd, LPARAM lParam) { // ... return static_cast<BOOL>(TRUE); // continue enumerating }, reinterpret_cast<LPARAM>(&myData)); Another use would be to write extern "C" callbacks for C routines. E.g.: my_class *pRes = static_cast<my_class*>(bsearch(&key, myClassObjectsArr, myClassObjectsArr_size, sizeof(my_class), extern "C" [](const void *pV1, const void *pV2) { const my_class& o1 = *static_cast<const my_class*>(pV1); const my_class& o2 = *static_cast<const my_class*>(pV2); int res; // ... return res; })); Is this possible?

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• Strategy for desugaring Haskell

  - by luqui

  I'm developing a virtual machine for purely functional programs, and I would like to be able to test and use the the wide variety of Haskell modules already available. The VM takes as input essentially terms in the untyped lambda calculus. I'm wondering what would be a good way to extract such a representation from modern Haskell modules (eg. with MPTC's, pattern guards, etc.). I did a little research and there doesn't seem to be a tool that does this already (I would be delighted to be mistaken), and that's okay. I'm looking for an approach. GHC Core seems too operationally focused, especially since one of the things the VM does is to change the evaluation order significantly. Are there any accessible intermediate representations that correspond more closely to the lambda calculus?

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• Interpreting regular expressions using find in Linux confusion

  - by PeanutsMonkey

  I am attempting to use the find command and came across an article at http://www.linux.ie/newusers/beginners-linux-guide/find.php which states The wildcard character is escaped with a slash so BASH sends a literal asterisk to the find utility as an argument instead of performing filename expansion and passing any number of files in as arguments. for the command find . -name up\*. Being new to the world of Linux I don't quite understand how the use of a backslash which is meant to escape the meta character * is interpreted and returns results as though as it is being passed to find. Does it mean if I use the -name option I have to use a backslash to pass a wildcard and if I don't use -name I don't have to use a backslash?

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• VBScript Regular Expressions to check IP address validity with some adtional characters

  - by yael

  How to create VB script Irregular expression syntax to check the VPparam (IP address validity) When the last octatat of the IP address is a range between ip's (x-y) and between each IP we can put the "," separator in order to add another IP example of VBparam VBparam=172.17.202.1-20 VBparam=172.17.202.1-10,192.9.200.1-100 VBparam=172.17.202.1-10,192.9.200.1-100,180.1.1.1-20 THX yael

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• Powershell: File copy/move with filename regular expressions?

  - by Ian Boyd

  i basically want to run: C:\>xcopy [0-9]{13}\.(gif|jpg|png) s:\TargetFolder /s i know xcopy doesn't support regular-expression filename searches. i am told that Powershell can do such a thing, although not given any syntax. Can anyone give the syntax of the above xcopy, but in PowerShell format?

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• Notepad++ Search & Replace with Regular Expressions

  - by Jeremy

  I know its simple, but I can't get it to work... I have a strings like {span style="display:none"}123{/span} and {span style="display:none"}456{/span} and {span style="display:none"}789{/span} in a file. I want to remove all of these string. So, I thought a simple regular expression replace in NotePad++ should be like "{span style="display:none"}[(.)]{/span}" - but, this is not working. Thank for your help!

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