R (complexity)
In computational complexity theory, R is the class of decision problems solvable by a Turing machine, which is the set of all recursive languages.
R is equal to the set of all total computable functions.
Since we can decide any problem for which there exists a recogniser and also a co-recogniser by simply interleaving them until one obtains a result, the class is equal to RE ∩ coRE.
...
Wikipedia