Are Recursively Enumerable Languages Decidable?

Yes. In particular, recursive (decidable) languages are a subset of the recursively enumerable languages, so anything that's not recursively enumerable isn't recursive (decidable).

Are programming languages recursively enumerable?

Yes, in fact, the recursively enumerable languages are also known as the Turing-recognizable languages. They are a strict superset of the decidable languages.

Which property of recursively enumerable sets is not decidable?

2 Answers. L is regular not closed for RE since this is Regularity property. L is finite not closed for RE since this is finiteness property.