All rings considered are commutative with unit. A ring R is SISI (in Vámos' terminology) if every subdirectly irreducible factor ring R/I is self-injective. SISI rings include Noetherian rings, Morita rings and almost maximal valuation rings ([V1]). In [F3] we raised the question of whether a polynomial ring R[x] over a SISI ring R is again SISI. In this paper we show this is not the case.

Let $P$ be a polynomial with integral coefficients. Shapiro showed that if the values of $P$ at infinitely many blocks of consecutive integers are of the form $Q\left(m\right)$, where $Q$ is a polynomial with integral coefficients, then $P\left(x\right)=Q\left(R\right(x\left)\right)$ for some polynomial $R$. In this paper, we show that if the values of $P$ at finitely many blocks of consecutive integers, each greater than a provided bound, are of the form $m^q$ where $q$ is an integer greater than 1, then $P\left(x\right)={\left(R\left(x\right)\right)}^q$ for some polynomial $R\left(x\right)$.

Let $K$ be a field and $S=K[x_1,...,x_n]$. Let $I$ be a monomial ideal of $S$ and $u_1,...,u_r$ be monomials in $S$. We prove that if $u_1,...,u_r$ form a filter-regular sequence on $S/I$, then $S/I$ is pretty clean if and only if $S/(I,u_1,...,u_r)$ is pretty clean. Also, we show that if $u_1,...,u_r$ form a filter-regular sequence on $S/I$, then Stanley’s conjecture is true for $S/I$ if and only if it is true for $S/(I,u_1,...,u_r)$. Finally, we prove that if $u_1,...,u_r$ is a minimal set of generators for $I$ which form either a $d$-sequence, proper sequence or strong $s$-sequence (with respect to the reverse lexicographic...

Soit $K$ un corps commutatif. Chercher une série formelle $S(X,T)\in K\left[\right[X,T\left]\right]$ vérifiant $S(X+Y,T)/S(X,T)\in K\left[\right[Y,T\left]\right]$ conduit naturellement à étudier l’application $U\left(T\right)\to \left(U\right(T){)}^X$, $U\left(T\right)$ étant une unité de l’algèbre $K\left[\right[T\left]\right]$, et à ramener les solutions à la forme $S(X,T)=\sum _{n\ge 0}{H}_n\left(X\right)T^n$, $\left(H_n\right(X\left)\right)$ étant une suite de $K\left[X\right]$ vérifiant les “identités multinomiales” :$$\left(\mu \right)H_n(X_1+...+X_k)=\sum _{{\alpha }_1+...+{\alpha }_k=n}{H}_{{\alpha }_1}(X_1)...H_{{\alpha }_k}(X_k\left)\right(n,k\ge 0).$$Après mise à l’écart par des lemmes combinatoires du cas caract$\left(K\right)\>0$ (les solutions sont triviales), on caractérise de plusieurs manières les solutions. On peut les faire coïncider avec l’ensemble NW des suites de polynômes (ou séries génératrices...