  Given the congruence lattice L of a finite algebra A with a Mal'cev term, we
look for those sequences of operations on L that are sequences of higher
commutator operations of expansions of A.
  The properties of higher commutators proved so far delimit the number of such
sequences: the number is always at most countably infinite; if it is infinite,
then L is the union of two proper subintervals with nonempty intersection.
