Myhill-nerode, Theory of Computation

Assignment Help:

Theorem (Myhill-Nerode) A language L ⊆ Σ is recognizable iff ≡L partitions Σ* into ?nitely many Nerode equivalence classes.

Proof: For the "only if" direction (that every recognizable language has ?nitely many Nerode equivalence classes) observe that L ∈ Recog iff L = L(A) for some DFA A and that if δ(q0,w) = δ(q0, u) (i.e., if the path from the start state labeled w and that labeled u end up at the same state) then w ≡L u. This is a consequence of the fact that the state ˆ δ(q0,w) encodes all the information the automaton remembers about the string w. If v extends w to wv ∈ L(A) then v is the label of a path to an accepting state from δ(q0,w). Since this is the same state as δ(q0, u) the same path witnesses that uv ∈ L. Similarly, if the path leads one to a non-accepting state then it must necessarily lead the other to the same state. The automaton has no way of distinguishing two strings that lead to the same state and, consequently, the language it recognizes cannot distinguish them. Since A is deterministic, every string in Σ* labels a path leading to some state, hence the equivalence classes corresponding to the states partition Σ*. Since the automaton has ?nitely many states, it distinguishes ?nitely many equivalence classes.


Related Discussions:- Myhill-nerode

Transition and path functions, When an FSA is deterministic the set of trip...

When an FSA is deterministic the set of triples encoding its edges represents a relation that is functional in its ?rst and third components: for every q and σ there is exactly one

Abstract model for an algorithm solving a problem, These assumptions hold f...

These assumptions hold for addition, for instance. Every instance of addition has a unique solution. Each instance is a pair of numbers and the possible solutions include any third

Strictly local generation automaton, Another way of interpreting a strictly...

Another way of interpreting a strictly local automaton is as a generator: a mechanism for building strings which is restricted to building all and only the automaton as an inexh

Finiteness problem for regular languages, The fact that the Recognition Pro...

The fact that the Recognition Problem is decidable gives us another algorithm for deciding Emptiness. The pumping lemma tells us that if every string x ∈ L(A) which has length grea

Union, Intuitively, closure of SL 2 under intersection is reasonably easy ...

Intuitively, closure of SL 2 under intersection is reasonably easy to see, particularly if one considers the Myhill graphs of the automata. Any path through both graphs will be a

Problem solving and programming concepts, The Last Stop Boutique is having ...

The Last Stop Boutique is having a five-day sale. Each day, starting on Monday, the price will drop 10% of the previous day’s price. For example, if the original price of a product

Trees and graphs , Trees and Graphs Overview: The problems for this ...

Trees and Graphs Overview: The problems for this assignment should be written up in a Mircosoft Word document. A scanned hand written file for the diagrams is also fine. Be

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd