Proteins can also be circularly permuted via post-translational modification, without permuting the underlying gene. The permutation group of formula 41 acts on this space by permuting the entries. Rejewski viewed the Enigma as permuting the plaintext letters into ciphertext. Any Latin square can be reduced by permuting (that is, reordering) the rows and columns. Consider the symmetric group formula 4 acting on R by permuting the coordinates. The symmetric group "S" acts on "R" by permuting the variables. Let "S" act on this tensor product space by permuting the indices. The braid is then represented in notation by permuting the labels of the indices. That is, formula 1 acts on formula 22 by permuting the standard basis vectors. Hence, Ghost Leg can be treated as a kind of permuting operator. In this case, the rules for permuting and (when using sets) contracting formulae are obsolete. By permuting the variables we get "n"!