Nerode equivalence

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Nerode equivalence An equivalence relation, =N, arising in formal language theory. It is defined analogously to the Myhill equivalence by the weaker properties:

for a language L over Σ, u =N u

if, for all w in Σ*, uwL iff uwL

and for a function f, u =N u

if, for all w in Σ*, f(uw) = f(uw)

Although coarser than the Myhill equivalence, it is finite only if the latter is. Unlike the latter, it gives only a right congruence: u =N u′ implies uv =N uv

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.

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Nerode equivalence

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