Next | Topology of Data Types | 8 |

Say that a

**set of strings**is semidecidable if membership in the set can be semidecided(This is equivalent to

*S*being recursively enumerable)Semidecidable sets are closed under binary intersection:

To semidecide A ∩ B:

if A(x): then if B(x): then YES else NO else NO

Next |