 
Summary: Origami Alignments and Constructions in the
Hyperbolic Plane
Roger C. Alperin
1 Introduction
Neutral geometry is the geometry made possible with the first 28 theorems of
Euclid's Book 1 those results which do not rely on the parallel postulate.
Hyperbolic geometry diverges from Euclidean geometry in that there are two
parallels (asymptotic) to a given line through a given point and infinitely many
other lines through the point which do not meet the given line (ultraparallel).
In hyperbolic geometry similar triangles are congruent; triangles have less than
180 degrees, there are no squares (regular four sided with 90 degree angles); the
area of a triangle is its defect (radian difference between and the angle sum).
As a consequence of this last remark, Bolyai (circa 1830) showed one can square
some circles (one uses a regular four sided polygon) in the hyperbolic plane using
ruler and compass, [G'04],[C'90], [J'95]. Our aim here is to introduce origami
constructions as a new method for doing geometry in the hyperbolic plane. We
discuss the use of origami for making any rulercompass construction and the
possibilities for other constructions which are not rulercompass constructions.
In the first section we give the alignments for folding in the hyperbolic plane.
These are the analogues of the classical origami axioms in the plane discussed by
