Random reals à la Chaitin with or without prefix freeness

VERÓNICA BECHER; SERGE GRIGORIEFF

THEORETICAL COMPUTER SCIENCE

Elsevier

Año: 2007 vol. 385 p. 193 - 201

0304-3975

Abstract.  We give a general theorem that provides examples of n-random reals a la Chaitin, for every natural number n; these are halting probabilities of partial computable functions that are universal by adjunction for the class of all partial computable functions, The same result holds for the class functions of partial computable functions with prefix-free domain. Thus, the usual technical requirement of prefix-freeness on domains is an option which we show to be non-critical when dealing with universality by adjunction. We also prove that the condition of universality by adjunction (which, though particular, is a very natural case of optimality) is essential in our theorem.