 Among the French mathematicians, the semi-intuitionist Borel (1908) introduced the distinction between effectively enumerable sets and denumerable ones. The Richard paradox is then solved by observing that Richard’s set \(E\) is certainly denumerable, because one can only determine at most a denumerable set of reals by finite means. Yet \(E\) is not effectively enumerable, i.e., one cannot produce with finitely many words a procedure for assigning unambiguously a rank (i.e., a position) to each element of the set. In order to make the enumeration of \(E\) effective, one ought to have solved all the mathematical problems which one could possibly state, because there are expressions which become definitions of a real only modulo a proof or solution of a certain problem. Borel has in mind a particular example: consider the expression “the unique transcendental number whose decimal expansion is obtained from that of \(\pi\) by replacing everywhere 7 with 8, and 8 with 7”. Of course, this is a good definition only if we have shown that the number is not algebraic (see Borel 1908. p. 446).