Regular Expression(RE)

• e is a RE

• a symbol in S is a RE

• Let r and s are REs.

  • (r) | (s) : or
  • (r)(s) : concatenation
  • (r)* : zero or more instances
  • (r)+ : one or more instances
  • (r)? : zero or one instance
  • [A-Z] : character classes

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