Abstract

There is a widespread delusion that in theoretical nuclear physics protons and neutrons are the real thing, and nucleons are not more than a mathematically equivalent formality. It is shown that, on the contrary, nucleons are the real thing, because only a part of the theory is essentially identical to proton-and-neutron theory, whereas the remaining part is physically relevant. The approach is general. Thus, this is a paradigm of relation of a wider and a more narrow theory, so that the wider theory describes reality better. Also the relation of disjoint domains to the exclusion principle is clarified. A general fermion theory of how to distinguish identical particles is presented.