Kneser’s theorem for upper Banach density
Journal de théorie des nombres de Bordeaux, Volume 18 (2006) no. 2, pp. 323-343.

Suppose A is a set of non-negative integers with upper Banach density α (see definition below) and the upper Banach density of A+A is less than 2α. We characterize the structure of A+A by showing the following: There is a positive integer g and a set W, which is the union of 2αg-1 arithmetic sequences [We call a set of the form a+d an arithmetic sequence of difference d and call a set of the form {a,a+d,a+2d,...,a+kd} an arithmetic progression of difference d. So an arithmetic progression is finite and an arithmetic sequence is infinite.] with the same difference g such that A+AW and if [a n ,b n ] for each n is an interval of integers such that b n -a n and the relative density of A in [a n ,b n ] approaches α, then there is an interval [c n ,d n ][a n ,b n ] for each n such that (d n -c n )/(b n -a n )1 and (A+A)[2c n ,2d n ]=W[2c n ,2d n ].

Supposons que A soit un ensemble d’entiers non négatifs avec densité de Banach supérieure α (voir définition plus bas) et que la densité de Banach supérieure de A+A soit inférieure à 2α. Nous caractérisons la structure de A+A en démontrant la proposition suivante : il existe un entier positif g et un ensemble W qui est l’union des [2αg-1] suites arithmétiques [We call a set of the form a+d an arithmetic sequence of difference d and call a set of the form {a,a+d,a+2d,...,a+kd} an arithmetic progression of difference d. So an arithmetic progression is finite and an arithmetic sequence is infinite.] avec la même différence g tels que A+AW et si [a n ,b n ] est, pour chaque n, un intervalle d’entiers tel que b n -a n et la densité relative de A dans [a n ,b n ] approche α, il existe alors un intervalle [c n ,d n ][a n ,b n ] pour chaque n tel que (d n -c n )/(b n -a n )1 et (A+A)[2c n ,2d n ]=W[2c n ,2d n ].

DOI: 10.5802/jtnb.547
Classification: 11B05, 11B13, 11U10, 03H15
Keywords: Upper Banach density, inverse problem, nonstandard analysis
Bihani, Prerna 1; Jin, Renling 2

1 Department of Mathematics University of Notre Dame Notre Dame, IN 46556, U.S.A.
2 Department of Mathematics College of Charleston Charleston, SC 29424, U.S.A.
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Bihani, Prerna; Jin, Renling. Kneser’s theorem for upper Banach density. Journal de théorie des nombres de Bordeaux, Volume 18 (2006) no. 2, pp. 323-343. doi : 10.5802/jtnb.547. http://www.numdam.org/articles/10.5802/jtnb.547/

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