Talk:Riesz sequence

The references to Planet Math are not useful, because the site seems to be down or malfunctioning. I added the Christensen reference, but it's not much helpful to the phrasing of the present wikipedia article. The Christensen article (pdf linked in the references section) has further references, but I can't access those now, so I'll have to come back to this. Any help on this might be appreciated, as this is my first Wikipedia edit! Tinqtaiya (talk) 01:25, 4 June 2015 (UTC)

What is ω in the condition 2. of the given theorem?