  We have undertaken a detailed analysis of HST/WFPC2 and STIS imaging
observations, and of supplementary wide-field ground-based observations
obtained with the NTT of two young ~10-25 Myr) compact star clusters in the
LMC, NGC 1805 and NGC 1818. The ultimate goal of our work is to improve our
understanding of the degree of primordial mass segregation in star clusters.
This is crucial for the interpretation of observational luminosity functions
(LFs) in terms of the initial mass function (IMF), and for constraining the
universality of the IMF.
  We present evidence for strong luminosity segregation in both clusters. The
LF slopes steepen with cluster radius; in both NGC 1805 and NGC 1818 the LF
slopes reach a stable level well beyond the clusters' core or half-light radii.
In addition, the brightest cluster stars are strongly concentrated within the
inner ~4 R_hl.
  The global cluster LF, although strongly nonlinear, is fairly well
approximated by the core or half-light LF; the (annular) LFs at these radii are
dominated by the segregated high-luminosity stars, however.
  We present tentative evidence for the presence of an excess number of bright
stars surrounding NGC 1818, for which we argue that they are most likely
massive stars that have been collisionally ejected from the cluster core. We
therefore suggest that the cores of massive young stars clusters undergo
significant dynamical evolution, even on time-scales as short as ~25 Myr.
