This article presents new data from a number of Germanic languages concerning the agreement patterns found in copular clauses that contain two nominais; in both clauses with specificational readings (such as The problem is your parents) and those with what are here termed readings of assumed identity (such as If I were you or In my dream I was you). It is argued that the specificational sentences involve asymmetric equative structures where one nominal is interpreted as in a concealed question, and that the cross-linguistic differences in agreement patterns found in the languages considered follow from the copula lexicalizing either Tense or a lower head.

Classically, in order to resolve an equation u ≈ v over a free monoid X*, we reduce it by a suitable family $\cal F$ of substitutions to a family of equations uf ≈ vf, $f\in\cal F$, each involving less variables than u ≈ v, and then combine solutions of uf ≈ vf into solutions of u ≈ v. The problem is to get $\cal F$ in a handy parametrized form. The method we propose consists in parametrizing the path traces in the so called graph of prime equations associated to u ≈ v. We carry out such a parametrization in the case the prime equations in the graph involve at most three variables.

This paper deals with a service system in which the processor must serve two types of impatient units. In the case of blocking, the first type units leave the system whereas the second type units enter a pool and wait to be processed later.

We develop an exhaustive analysis of the system including embedded Markov chain, fundamental period and various classical stationary probability distributions. More specific performance measures, such as the number of lost customers and other quantities, are also considered. The mathematical analysis of the model is based on the theory of Markov renewal processes, in Markov chains of M/G/l type and in expressions of ‘Takács' equation' type.