  We analyze the structure of the Fundamental Measure Theory for the free
energy density functional of hard sphere mixtures. A comparative study of the
different versions of the theory, and other density functional approaches, is
done in terms of their generic form for the three-points direct correlation
function, which shows clearly the main advantages and problems of the different
approximations. A recently developed version for the monocomponent case is
extended to mixtures of hard spheres with different radii, and a new
prescription is presented to obtain the exact dimensional crossover of those
mixtures in the one-dimensional (1D) limit. Numerical results for planar
wall-fluid interfaces and for the 1D fluid are presented.
