Decidable

• Another example:

• The language 0n1n is decidable:

  • If the tape is empty, ACCEPT
  • Otherwise, if the input does not look like 0* 1*, REJECT
  • Cross off the first 0. Then move right until the first 1 (not crossed off)
  • Cross off that 1, then move left until the first 0.
  • Repeat the above 2 steps until we run out of 0’s or 1’s
    • If there are more 0’s than 1’s REJECT
    • If there are more 1’s than 0’s REJECT
    • If there are an equal number, ACCEPT

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