There exist non regular expressions such as a n b n n

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There exist non-regular expressions such as { a n b n | n 0} {(0, 1)*(01) n (0, 1)*(10) n (0,1)*1 | n 0} Table 2.1 Regular Expression Identities φ * = λ ; The * operation puts together any number of strings from the language to get a (new) string in the result. If the language is empty, the * operation can put together 0 strings, giving only the null string ( λ ). φ u = u φ = φ ; Concatenating φ to any set yields φ . ( a , λ )( b , λ ) = { λ , a , b , ab }. The regular expression c *( b , ac *)* yields all strings that do not contain the substring bc . How about c *( b , ac *)*?
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15 Grammars Languages and Accepting Machines Grammars Languages Accepting Machines Type 0 grammars, Recursively TM Phrase-structure grammars, enumerable NDTM Unrestricted grammars Unrestricted Type 1 grammars, Contest-sensitive Linear-bounded Context-sensitive grammars, languages Automata Monotonic grammars Type 2 grammars, Context-free PDA Context-free grammars languages Type 3 grammars, Regular FSA Regular grammars, languages NDFA Left-linear grammars, Right-linear grammars
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  • Winter '12
  • DennisNg
  • Formal language, Regular expression, σ, Defn, regular sets

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