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Matching lattice QC+ED to Nature

The first step of any QFT calculation, aiming at phenomenological predictions, is the matching of the theory to Nature. The matching procedure fixes the parameters of the theory in terms of an equal number of external inputs that, if the theory is expected to reproduce observations, must be experimentally measured physical quantities. At the sub-percent level of accuracy QED radiative corrections become important and the theory expected to describe the hadronic Universe is QCD+QED. Phenomenological predictions deriving from lattice QCD calculations do depend, at this level of precision, upon the choice of the external inputs used to match/define the approximate theory. In this written version of my talk I concentrate on the theoretical aspects of the matching procedure of lattice QCD$+$QED and of the definition of QCD, strongly advocating a community agreement on the matching scheme to be used in future lattice QCD calculations.