Nerds don't code in Flash. :bleh: Nerds do Fortran.
(Nah I never learnt Fortran.)
You don't need to detect collisions in this case, the bodies can't move freely. The equations describe their movement and their solution will simply yield the positions of all solids--of course compliant with the boundary conditions that were inserted in those same equations.
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This retro zombie fashion is getting old :P