Let $X\cong C^n$, let $M$ be a $C^2$ hypersurface of $X$, $S$ be a $C^2$ submanifold of $M$. Denote by $L_M$ the Levi form of $M$ at $z_0\in S$. In a previous paper [3] two numbers $s^{\pm }\left(S,p\right)$, $p\in {\left({\dot{T}}_S^{*}X\right)}_{z_0}$ are defined; for $S=M$ they are the numbers of positive and negative eigenvalues for $L_M$. For $S\subset M$, $p\in S\times {}_M\dot{T}{}^{*}{}_{S}X)$, we show here that $s^{\pm }\left(S,p\right)$ are still the numbers of positive and negative eigenvalues for $L_M$ when restricted to $T_{z_0}^{C}S$. Applications to the concentration in degree for microfunctions at the boundary are given.

We prove a general theorem about preservation of the covering dimension $dim$ by certain covariant functors that implies, among others, the following concrete results. If $G$ G is a pathwise connected...

An extension $D\subseteq R$ of integral domains is $t$- (resp., $t$-) if ${\left(IR\right)}^{-1}={\left(I^{-1}R\right)}_v$ (resp., ${\left(IR\right)}_v={\left(I_{v}R\right)}_v)$ for every nonzero finitely generated fractional ideal $I$ of $D$. We show that strongly $t$-compatible implies $t$-compatible and give examples to show that the converse does not hold. We also indicate situations where strong $t$-compatibility and its variants show up naturally. In addition, we study integral domains $D$ such that $D\subseteq R$ is strongly $t$-compatible (resp., $t$-compatible) for every overring $R$ of $D$. ...

Sia $X\subset {\mathbf{P}}^N$ una varietà irriducibile $n$-dimensionale localmente Cohen-Macaulay, $\mathbf{Q}$-Gorenstein e non di tipo generale; assumiamo $N=6$, $2n=N+2$ e $\text{dim}\left(\text{Sing}\left(X\right)\right)=2n-N$. In questo lavoro dimostriamo che $\text{deg}\left(X\right)\le {\left(N+1\right)}^{N-n}$ e quindi che l'insieme di tutte queste varietà è parametrizzato da un insieme finito di varietà algebriche.

Let $C_F\left(X\right)$ be the socle of C(X). It is shown that each prime ideal in $C\left(X\right)/C_F\left(X\right)$ is essential. For each h ∈ C(X), we prove that every prime ideal (resp. z-ideal) of C(X)/(h) is essential if and only if the set Z(h) of zeros of h contains no isolated points (resp. int Z(h) = ∅). It is proved that $dim(C\left(X\right)/C_F\left(X\right))\ge dimC\left(X\right)$, where dim C(X) denotes the Goldie dimension of C(X), and the inequality may be strict. We also give an algebraic characterization of compact spaces with at most a countable number of nonisolated points....

We prove that if f: X → Y is a closed surjective map between metric spaces such that every fiber $f^{-1}\left(y\right)$ belongs to a class S of spaces, then there exists an $F_{\sigma }$-set A ⊂ X such that A ∈ S and $dim{f}^{-1}\left(y\right)\setminus A=0$ for all y ∈ Y. Here, S can be one of the following classes: (i) M: e-dim M ≤ K for some CW-complex K; (ii) C-spaces; (iii) weakly infinite-dimensional spaces. We also establish that if S = M: dim M ≤ n, then dim f ∆ g ≤ 0 for almost all $g\in C\left(X{,}^{n+1}\right)$.

Nel presente lavoro si studiano le applicazioni polinomiali proprie $$\phi :{\mathbb{R}}^n\to {\mathbb{R}}^q.$$ In particolare si prova: 1) se $\phi :{\mathbb{R}}^n\to \mathbb{R}$ è un'applicazione polinomiale tale che ${\phi }^{-1}\left(y\right)$ è compatto per ogni $y\in \mathbb{R}$, allora $\phi$ è propria; 2) se $\phi :{\mathbb{R}}^n\to {\mathbb{R}}^q$ è polinomiale a fibra compatta e $\phi \left({\mathbb{R}}^n\right)$ è chiuso in ${\mathbb{R}}^q$ allora $\phi$ è propria; 3) l'insieme delle applicazioni polinomiali proprie di ${\mathbb{R}}^n$ in ${\mathbb{R}}^q$ è denso, nella topologia $C^{\mathrm{\infty }}$, nello spazio delle applicazioni $C^{\mathrm{\infty }}$ di ${\mathbb{R}}^n$ in ${\mathbb{R}}^q$.