Published online by Cambridge University Press: 09 January 2018
In this article, a notion of Schauder equivalence relation ℝℕ/L is introduced, where L is a linear subspace of ℝℕ and the unit vectors form a Schauder basis of L. The main theorem is to show that the following conditions are equivalent:
(1) the unit vector basis is boundedly complete;
(2) L is a F σ in ℝℕ;
(3) ℝℕ/L is Borel reducible to ℓ ∞.
We show that any Schauder equivalence relation generalized by a basis of ℓ 2 is Borel bireducible to ℝℕ/ℓ 2 itself, but it is not true for bases of c 0 or ℓ 1. Furthermore, among all Schauder equivalence relations generated by sequences in c 0, we find the minimum and the maximum elements with respect to Borel reducibility.