On the Geometry of Müntz Spaces

LetΛ={λk}k=1∞satisfy0<λ1<λ2<⋯,∑k=1∞‍1/λk<∞andinfk(λk+1-λk)>0. We investigate the Müntz spacesMpΛ=span¯{tλk:k=1,2,…}⊂Lp(0,1)for1≤p≤∞. We show that, for eachp, there is a Müntz spaceFpwhich contains isomorphic copies of all Müntz spaces as complemented subspaces.Fpis uniquely determined up to isomorphisms by this maximality property. We discuss explicit descriptions ofFp. In particularFpis isomorphic to a Müntz spaceMp(Λ^)whereΛ^consists of positive integers. Finally we show that the Banach spaces(∑n‍⊕Fn)pfor1≤p<∞and(∑n‍⊕Fn)0forp=∞are always isomorphic to suitable Müntz spacesMp(Λ)if theFnare the spans of arbitrary finitely many monomials over[0,1].