Language and Grammars (2)

• An infinite number of sentences can be expresses by a finite number of productions by using recursion over some symbols.
• Example:
  Number = Digit | Digit Number.
  Digit  = "0" | "1" | "2" | "3" | "4" | "5" |  "6" | "7" | "8" | "9".
• allows
  0 | 12 | 347 | 0013 | ...