Abstract:
We point out an existence criterion for positive computable total
$\Pi^1_1$-numberings of families of subsets of a given
$\Pi^1_1$-set. In
particular, it is stated that the family of all
$\Pi^1_1$-sets has no
positive computable total
$\Pi^1_1$-numberings. Also we obtain a criterion
of existence for computable Friedberg
$\Sigma^1_1$-numberings of families of
subsets of a given
$\Sigma^1_1$-set, the consequence of which is the absence
of a computable Friedberg
$\Sigma^1_1$-numbering of the family of all
$\Sigma^1_1$-sets. Questions concerning the existence of negative computable
$\Pi^1_1$- and $\Sigma^1_1$-numberings of the families mentioned are considered.