The possibility of applying the Treiman-Yang criterion to the study of such reactions as n+p→p+p+π- is discussed. For this, the contributions, from all possible one-pion exchange Feynman graphs, to the definite final state are considered. This allows one to single out from experimental data events corresponsing to some Feynman graph. Such an approach makes it possible to apply the Treiman-Yang criterion also to processes in which there are identical particles in the final state.