  We analyze a system of fermions in a one-dimensional harmonic trap with
attractive delta-interactions between different fermions species, as an
approximate description of experiments involving atomic dimers. We solve the
problem of two fermion pairs numerically using the so-called ''coboson
formalism'' as an alternative to techniques which are based on the
single-particle basis. This allows us to explore the strongly bound regime,
approaching the limit of infinite attraction in which the composite particles
behave as hard-core bosons. Our procedure is computationally inexpensive and
illustrates how the coboson toolbox is useful for ultracold atom systems even
in absence of condensation.
