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                          xlink:from="ifrs-full_NoncurrentLiabilities"
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                            order="19.0"
                          xlink:type="arc"/>
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                          xlink:from="ifrs-full_NoncurrentLiabilities"
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      <link:loc xlink:href="http://xbrl.ifrs.org/taxonomy/2020-03-16/full_ifrs/full_ifrs-cor_2020-03-16.xsd#ifrs-full_OtherNoncurrentFinancialLiabilities" xlink:label="ifrs-full_OtherNoncurrentFinancialLiabilities" xlink:type="locator"/>
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                          xlink:from="ifrs-full_NoncurrentLiabilities"
                          xlink:to="ifrs-full_OtherNoncurrentFinancialLiabilities"
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      <link:loc xlink:href="815600F4A5F5D3BCD688-2021-12-31.xsd#ext_NonCurrentPayablesDueToBanksCorrect" xlink:label="ext_NonCurrentPayablesDueToBanksCorrect" xlink:type="locator"/>
      <link:calculationArc
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      <link:loc xlink:href="815600F4A5F5D3BCD688-2021-12-31.xsd#ext_NoncurrentFinancialLiabilitiesForRightsOfUseCorrect" xlink:label="ext_NoncurrentFinancialLiabilitiesForRightsOfUseCorrect" xlink:type="locator"/>
      <link:calculationArc
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      <link:calculationArc
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                          xlink:from="ifrs-full_Assets"
                          xlink:to="ifrs-full_NoncurrentAssets"
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      <link:calculationArc
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                          xlink:from="ifrs-full_Assets"
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                          xlink:from="ifrs-full_NoncurrentAssets"
                          xlink:to="ifrs-full_PropertyPlantAndEquipment"
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      <link:loc xlink:href="http://xbrl.ifrs.org/taxonomy/2020-03-16/full_ifrs/full_ifrs-cor_2020-03-16.xsd#ifrs-full_InvestmentAccountedForUsingEquityMethod" xlink:label="ifrs-full_InvestmentAccountedForUsingEquityMethod" xlink:type="locator"/>
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