We prove necessary and sufficient conditions for the validity of the classical chain rule in the Sobolev space $W_{\text{loc}}^{1,1}({ℝ}^N;{ℝ}^d)$ and in the space $B{V}_{\text{loc}}({ℝ}^N;{ℝ}^d)$ of functions of bounded variation.

We collect known and prove new necessary and sufficient conditions for the weighted weak type maximal inequality of the form $${\Phi }_1\left(\lambda \right)\varrho \left(\{x\in X:M_{\mu }f\left(x\right)>\lambda \}\right)\le c{\int }_X{\Phi }_2\left(c\right|f\left(x\right)\left|\right)\sigma \left(x\right)\mathrm{d}\mu \left(x\right),$$ which extends some known results.

A necessary condition for Kostyuchenko type systems and system of powers to be a basis in $L_p$ (1 ≤ p < +∞) spaces is obtained. In particular, we find a necessary condition for a Kostyuchenko system to be a basis in $L_p$ (1 ≤ p < +∞).

For Tychonoff $X$ and $\alpha$ an infinite cardinal, let $\alpha defX:=$ the minimum number of $\alpha$ cozero-sets of the Čech-Stone compactification which intersect to $X$ (generalizing $ℝ$-defect), and let $rtX:={min}_{\alpha }max(\alpha ,\alpha defX)$. Give $C\left(X\right)$ the compact-open topology. It is shown that $\tau C\left(X\right)\le n\chi C\left(X\right)\le rtX=max\left(L\right(X),L(X)defX)$, where: $\tau$ is tightness; $n\chi$ is the network character; $L\left(X\right)$ is the Lindel"of number. For example, it follows that, for $X$ Čech-complete, $\tau C\left(X\right)=L\left(X\right)$. The (apparently new) cardinal functions $n\chi C$ and $rt$ are compared with several others.

The Nevanlinna algebras, ${}_{\alpha }^p$, of this paper are the $L^p$ variants of classical weighted area Nevanlinna classes of analytic functions on = z ∈ ℂ: |z| < 1. They are F-algebras, neither locally bounded nor locally convex, with a rich duality structure. For s = (α+2)/p, the algebra $F_s$ of analytic functions f: → ℂ such that ${(1-|z\left|\right)}^s\left|f\left(z\right)\right|\to 0$ as |z| → 1 is the Fréchet envelope of ${}_{\alpha }^p$. The corresponding algebra ${}_s^{\infty }$ of analytic f: → ℂ such that $su{p}_{z\in }{(1-|z\left|\right)}^s\left|f\left(z\right)\right|<\infty$ is a complete metric space but fails to be a topological vector space. $F_s$ is also...

We give a new Calderón-Zygmund decomposition for Sobolev spaces on a doubling Riemannian manifold. Our hypotheses are weaker than those of the already known decomposition which used classical Poincaré inequalities.