ACTA ARITHMETICA

for quadratic numbers by Christian Faivre (Marseille) 0. Introduction. Let x be an irrational number. We will denote by [a0(x),..., an(x),...] its regular continued fraction expansion and by pn(x)/qn(x) = [a0(x),..., an(x)] the nth convergent. The famous Theorem of P. Lévy [12] states that for almost all x ∈ R (in the sense of Lebesgue) we hav