  Probabilities to find a chosen number of electrons in flexible domains of
space are calculated for highly correlated wave functions. Quantum mechanics
can produce higher probabilities for chemically relevant arrangements of
electrons in these regions. However, the probability to have a given
arrangement, e.g., that corresponding to chemical formulas (bonds or atoms), is
low although being often maximal. Like in valence bond theory, it is useful to
consider alternative distributions of the electrons. Exchanges of electrons
should be considered not only between atoms, but also between other types of
regions, like those attributed to lone pairs. It is useful to have definitions
flexible enough to allow the user to find the reference representations he
considers most relevant. We tentatively suggest a tool (the effective number of
parties) to help one make the choice.
