  In this paper, we investigate the possibility to deterministically solve the
gathering problem (GP) with weak robots (anonymous, autonomous, disoriented,
deaf and dumb, and oblivious). We introduce strong multiplicity detection as
the ability for the robots to detect the exact number of robots located at a
given position. We show that with strong multiplicity detection, there exists a
deterministic self-stabilizing algorithm solving GP for n robots if, and only
if, n is odd.
