  The eigenfunctions of electronic Hamiltonians determine the stable structures
and dynamics of molecules through the local distributions of their densities.
In this paper an a priori upper bound for such local distributions of the
densities is given. The bound means that concentration of electrons is
prohibited due to the repulsion between the electrons. A relation between
one-electron and two-electron densities resulting from the antisymmetry of the
eigenfunctions plays a crucial role in the proof.
