Published online by Cambridge University Press: 02 November 2012
Motivated by mathematical aspects of origami, Erik Demaine asked which points in the plane can be constructed by using lines whose angles are multiples of $\pi /n$ for some fixed
$n$. This has been answered for some specific small values of
$n$ including
$n=3,4,5,6,8,10,12,24$. We answer this question for arbitrary
$n$. The set of points is a subring of the complex plane
$\mathbf {C}$, lying inside the cyclotomic field of
$n$th roots of unity; the precise description of the ring depends on whether
$n$is prime or composite. The techniques apply in more general situations, for example, infinite sets of angles, or more general constructions of subsets of the plane.