  Simulations with Aarseth's (1994) NBODY5 code are presented of an initially
dense binary-rich cluster. It is assumed that the star formation efficiency is
50 per cent with instantaneous mass loss. The model central density and
velocity dispersion agree with the observational constraints if expansion is
only about 6x10^4 yr old. Additionally, the observed binary proportion
constrains the primordial proportion to have been significantly less than in
Taurus--Auriga. The claim that a variation of the birth binary proportion with
gas cloud parameters has been detected, however, can only be verified if the
cluster can be shown to be expanding rapidly.
