  Unlabelled Necklaces are an equivalence class of cyclic words under both the
rotation (cyclic shift) and the relabelling operations. The relabelling of a
word is a bijective mapping from the alphabet to itself. The main result of the
paper is the first polynomial-time algorithm for ranking unlabelled necklaces
of a binary alphabet. The time-complexity of the algorithm is $O(n^6 \log^2
n)$, where $n$ is the length of the considered necklaces. The key part of the
algorithm is to compute the rank of any word with respect to the set of
unlabelled necklaces by finding three other ranks: the rank over all necklaces,
the rank over symmetric unlabelled necklaces, and the rank over necklaces with
an enclosing labelling. The last two concepts are introduced in this paper.
