  For some values of the constituent masses m_i, the hydrogen-like molecule
(m_1^+,m_2^+,m_3^-,m_4^-) is stable with respect to spontaneous dissociation
into two neutral atoms, while none of its three-body subsystems such as
(m_1^+,m_2^+,m_3^-) is stable. This occurs in particular in the neighbourhood
of the (M^+,m^+,M^-,m^-) configuration with M/m=2, as for instance for the
molecule (p,d,\bar{p},\bar{d}) involving an antiproton and an antideuteron.
