https://root.cern.ch/doc/master/structTMVA_1_1Experimental_1_1SOFIE_1_1NaryOperatorTraits_3_01float_00_01EBasicNaryOperator_1_1Mean_01_4.html
ROOT: TMVA::Experimental::SOFIE::NaryOperatorTraits float, EBasicNaryOperator::Mean Struct...
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