  Emission of two neutrons or two protons in reactions and decays is often
discussed in terms of "dineutron" or "diproton" emission. The discussion often
leans intuitively on something described by Migdal-Watson approximation. In
this work we propose a way to formalize situations of dineutron emission. It is
demonstrated that properly formally defined dineutron emission may reveal
properties which are drastically different from those traditionally expected,
and properties which are actually observed in three-body decays.
