S. Ben-David, K. Meer and C. Michaux
This note deals with the structure of the class $N_R$ introduced by Blum, Shub and Smale. It is shown that, assuming $N_R$ is not included in the class $P_R$/poly , there exists a problem in $N_R$ which does not belong to $P_R$/poly and which is not $N_R$-complete. It also clarifies the scope of a padding technique used in a former similar result by Ladner concerning the structure of the class NP (in the common, Turing machine, model).