The purpose of this paper is to present a method for treating uniformly a large number of enumeration problems involving sequences over a finite alphabet subject to general restrictions. Many of these problems are classical in origin, including the Mrnage problem (Lucas [16]), the alternating permutation problem (Netto [19], Andr6 [1, 2]), the derangement problem (Montmort [18]), and more recen...

In science, it is a common experience to discover that although the investigated effect is very clear in some individuals, statistical tests are not significant because the effect is null or even opposite in other individuals. Indeed, t-tests, Anovas and linear regressions compare the average effect with respect to its inter-individual variability, so that they can fail to evidence a factor tha...