An equivalence relation, =N, arising in formal language theory. It is defined analogously to the Myhill equivalence by the weaker properties:
Although coarser than the Myhill equivalence, it is finite only if the latter is. Unlike the latter, it gives only a right congruence:
and thus does not give rise to a semigroup. The number of equivalence classes is the number of states in the minimal machine for
L.