Quantifier elimination in ordered abelian groups
  We give a new proof of quantifier elimination in the theory of all ordered abelian groups in a suitable language. More precisely, this is only "quantifier elimination relative to ordered sets" in the following sense. Each definable set in the group is a union of a family of quantifier free definable sets, where the parameter of the family runs over a set definable (with quantifiers) in a sort which carries the structure of an ordered set with some additional unary predicates.   As a corollary, we find that all definable functions in ordered abelian groups are piecewise affine linear on finitely many definable pieces. 
Raf Cluckers and Immanuel Halupczok
math.LO