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Myhill-Nerode Theorem

Logic and Foundations

The Myhill-Nerode Theorem provides a necessary and sufficient condition for a formal language to be regular, characterizing regularity in terms of the number of equivalence classes formed by an equivalence relation defined on strings by their future behavior with respect to the language. Named for John Myhill and Anil Nerode, who proved it at the University of Chicago in 1957, it is a foundational result of automata theory used both to prove that particular languages are regular and, via the same equivalence classes, to construct the smallest possible deterministic finite automaton recognizing a given regular language.

Facts
Statement
A language L is regular if and only if its Myhill-Nerode relation has a finite number of equivalence classes, and this number equals the number of states in the minimal deterministic finite automaton accepting L. 1
Proof Year
1957 1
Classification
Statement Form
Identity or Equation 1
Statement Form
Characterization Theorem 1
Connections

In Branch

Sources
1. Myhill-Nerode theorem (Wikipedia)
  • Statement
    that this number is equal to the number of states in the minimal deterministic finite automaton (DFA) accepting L.
  • History
    proved it at the University of Chicago in 1957
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