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<p class="MsoNormal"><span lang="EN-US">This is really cool for both erlang and elixir<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">defmodule MyBianry do<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">def size({_, binary}) do<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">:erlang.size(binary)
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> end
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">end<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">defmodule MyTuple do<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">def size({_, tuple} ) do<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">:erlang.size(tuple)
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> end
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">end<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">defmodule MyList do<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">def size({_, list}) do<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">length(list)
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> end
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">end<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(24)> var={MyBianry, <<1,2,3,4>>}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">{MyBianry, <<1, 2, 3, 4>>}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(25)> var.size
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">4<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(26)> var={MyTuple, {1,2,3,4}}
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">{MyTuple, {1, 2, 3, 4}}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(27)> var.size
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">4<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(28)> var={MyList, [1,2,3,4,5,6]}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">{MyList, [1, 2, 3, 4, 5, 6]}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(29)> var.size
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">6<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(9)> c "myList.erl"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">[:myList]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(10)> c "myBinary.erl"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">[:myBinary]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(11)> c "myTuple.erl"
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">[:myTuple]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(12)> :myList.msize({:a,[1,2,3,4]})<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">4<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(13)> var={:myList,[1,2,3,4]}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">{:myList, [1, 2, 3, 4]}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(14)> var.msize<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">4<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(15)> var={:myBinary,<<1,2,3,4>>}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">{:myBinary, <<1, 2, 3, 4>>}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(16)> var.msize
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">4<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(17)> var={:myTuple,{1,2,3,4}} <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">{:myTuple, {1, 2, 3, 4}}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(18)> var.msize
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">4<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">iex(19)>
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal">发送自<span lang="EN-US"> Windows 10 </span>版<span lang="EN-US"><a href="https://go.microsoft.com/fwlink/?LinkId=550986"><span lang="EN-US"><span lang="EN-US">邮件</span></span></a></span>应用</p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
<div style="mso-element:para-border-div;border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal" style="border:none;padding:0cm"><b>发件人<span lang="EN-US">: </span>
</b><span lang="EN-US"><a href="mailto:jose.valim@plataformatec.com.br">José Valim</a><br>
</span><b>发送时间<span lang="EN-US">: </span></b><span lang="EN-US">2017</span>年<span lang="EN-US">4</span>月<span lang="EN-US">14</span>日<span lang="EN-US"> 20:13<br>
</span><b>收件人<span lang="EN-US">: </span></b><span lang="EN-US"><a href="mailto:erlang-questions@erlang.org">Erlang</a><br>
</span><b>主题<span lang="EN-US">: </span></b><span lang="EN-US">[erlang-questions] Proposal to remove tuple dispatches from Erlang</span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">Hi everyone,
</span><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">I would like to propose to remove "tuple dispatches" from Erlang.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">The tuple dispatch is the ability to invoke a function or call erlang:apply/3 on a tuple as first argument:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">Eshell V9.0 (abort with ^G)<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">1> Var = dict:new().<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">{dict,0,16,16,8,80,48,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"> {[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"> {{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]}}}<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">2> Var:size().<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">0<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">This behaviour is considered by most in the community to be undesired and confusing, as it obfuscates the meaning of the code and adds indirection.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">I have also heard this behaviour made it harder to add some optimizations to the VM. I would love if someone more knowledgeable on the area could confirm or deny this. If true,
it is also a strong argument to remove such behaviour.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">Another reason for removing it is that the behaviour can be implemented as needed by adding is_tuple/1 checks to the code or more programmatically by using a parse transforms
(see note 1 at the bottom for a limitation though). Therefore those who need the behaviour can include it only when necessary and we don't impose it as a semantics to the whole language (and ecosystem).<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">I can think of two strategies for removing the behaviour:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">1. Clean-cut: the code responsible for tuple dispatching will be completely removed from the VM and a parse transform will be made available. The parse transform could be part
of Erlang/OTP or a separate repository. This change is backwards incompatible at the BEAM level. Code that relies on tuple dispatch without the parse transform on OTP 19 will not work on OTP 20. However, the parse transform should work with any OTP version,
so if the parse transform is used during compilation, the code is guaranteed to work on OTP 19 and earlier as well as on OTP 20 onwards.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">2. New byte codes: if we don't want to break backwards compatibility at the BEAM level, I believe our only option is to introduce new bytecodes and a new apply BIF. Usage of
the old BIFs and bytecode could emit warnings while we phase them out. A compiler option or parse transform should still be made available if a developer relying on those features wants their code to run without warnings.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">Please let me know if there are other options available,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">I will be glad to send patches and implement the required parse-transforms if this is accepted by the OTP team.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:SimSun"><br>
José Valim</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:SimSun"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Verdana",sans-serif"><a href="http://www.plataformatec.com.br/" target="_blank"><span style="color:#2A5DB0">www.plataformatec.com.br</span></a></span><span lang="EN-US" style="font-size:10.0pt;font-family:SimSun"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Verdana",sans-serif">Skype: jv.ptec</span><span lang="EN-US" style="font-size:10.0pt;font-family:SimSun"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Verdana",sans-serif">Founder and Director of R&D</span><span lang="EN-US" style="font-size:10.0pt;font-family:SimSun"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">Note 1. A parse-transform would be unable to make the following code work in the same way as today:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">erlang:apply(erlang, apply, [dict:new(), size, []])<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun">Although I would consider it highly unlikely to exist so it should not be a point of contention.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
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