Recognizable
A language is recognizable if some TM accepts every string in that language (and no strings that are not)
- Such a TM is called a recognizer
-
L = { Ok | k = 2n for some n }
Hilbert’s 10th problem:
- Try all possible tuples of integers.
- If one is a root of the polynomial, ACCEPT
HALT = { <M,w> | M is the encoding of a valid TM, and M halts (eventually) on input w }
- Simulate M on input w.
- If M halts, then ACCEPT