  The $A$-dependence of the bond energy $\Delta B_{\Lambda\Lambda}$ of the
${\Lambda\Lambda}$ hypernuclear ground states is calculated in a three-body
${\Lambda + \Lambda + {^{A}Z}}$ model and in the Skyrme-Hartree-Fock approach.
Various ${\Lambda\Lambda}$ and $\Lambda$-nucleus or ${\Lambda N}$ potentials
are used and the sensitivity of $\Delta B_{\Lambda\Lambda}$ to the interactions
is discussed. It is shown that in medium and heavy ${\Lambda\Lambda}$
hypernuclei, $\Delta B_{\Lambda\Lambda}$ is a linear function of
$r_{\Lambda}^{-3}$, where $r_\Lambda$ is rms radius of the hyperon orbital. It
looks unlikely that it will be possible to extract ${\Lambda\Lambda}$
interaction from the double-$\Lambda$ hypernuclear energies only, the
additional information about the $\Lambda$-core interaction, in particular, on
$r_{\Lambda}$ is needed.
