On linear combinations of units with bounded coefficients and   double-base digit expansions
  Let $\ord$ be the maximal order of a number field. Belcher showed in the 1970s that every algebraic integer in $\ord$ is the sum of pairwise distinct units, if the unit equation $u+v=2$ has a non-trivial solution $u,v\in\ord^*$. We generalize this result and give applications to signed double-base digit expansions. 
Daniel Krenn, J\"org Thuswaldner, Volker Ziegler
math.NT