Abstract.- The computation domain.- Recursion on ?.- Connection with Kleene recursion in higher types.- Recursion in normal lists on ?.- Kleene recursion in normal objects of type n+2, n>0.- Computation theories on ?.- Abstract Kleene theories.- Normal computation theories on ?.- More about Mahloness.- Calculation of the lengths of some computations.- Gaps.- On platek: ¿Foundations of recursion theory¿.- A final comment concerning the two types.