On some Fréchet spaces associated to the functions satisfying Mulholland inequality

In this article we explore a new growth condition on Young functions, which we call Mulholland condition, pertaining to the mathematician H.P Mulholland, who studied these functions for the first time, albeit in a different context. We construct a non-trivial Young function $Ω$ which satisfies Mulholland condition and $Δ_2$-condition. We then associate exotic $F$-norms to the vector space $X_1\oplus X_2$, where $X_1$ and $X_2$ are Banach spaces, using the function $Ω$. This $F$-spaces contains the Banach space $X_1$ and $X_2$ as a maximal Banach subspace. Further, the Banach envelope $(X_1\oplus X_2,||.||{Ω_o})$ of this $F$-space corresponds to the Young function $Ω_o$ who characteristic function is an asymptotic line to the characteristic function of the Young function $Ω$. Thus these $F$-spaces serves as “interpolation space” for Banach spaces $X_1$ and $(X_1\oplus X_2, ||.||{Ω_o})$ in some sense. These $F$-space are well behaved in regards to Hahn-Banach extension property, which is lacking in classical $F$-spaces like $L^p$ and $H^p$ for $0<p<1$. Towards the end, some direct sums for Orlicz spaces are discussed.

💡 Research Summary

The paper introduces a novel growth restriction for Young functions, called the Mulholland condition, and uses it to construct a new class of F‑spaces that interpolate between Banach spaces. A Young function Φ satisfies the Mulholland condition if it is continuous, strictly increasing on