  In the unsplittable capacitated vehicle routing problem, we are given a
metric space with a vertex called depot and a set of vertices called terminals.
Each terminal is associated with a positive demand between 0 and 1. The goal is
to find a minimum length collection of tours starting and ending at the depot
such that the demand of each terminal is covered by a single tour (i.e., the
demand cannot be split), and the total demand of the terminals in each tour
does not exceed the capacity of 1.
  Our main result is a polynomial-time $(2+\epsilon)$-approximation algorithm
for this problem in the two-dimensional Euclidean plane, i.e., for the special
case where the terminals and the depot are associated with points in the
Euclidean plane and their distances are defined accordingly. This improves on
recent work by Blauth, Traub, and Vygen [IPCO'21] and Friggstad, Mousavi,
Rahgoshay, and Salavatipour [IPCO'22].
