Non-Minimality of the Width-$w$ Non-adjacent Form in Conjunction with   Trace One $\tau$-adic Digit Expansions and Koblitz Curves in Characteristic   Two
  This article deals with redundant digit expansions with an imaginary quadratic algebraic integer with trace $\pm 1$ as base and a minimal norm representatives digit set. For $w\geq 2$ it is shown that the width-$w$ non-adjacent form is not an optimal expansion, meaning that it does not minimize the (Hamming-)weight among all possible expansions with the same digit set. One main part of the proof uses tools from Diophantine analysis, namely the theory of linear forms in logarithms and the Baker--Davenport reduction method. 
Daniel Krenn and Volker Ziegler
math.NT