Folding maps on a cross-cap

Abstract

We study the reflectional symmetry of a surface in the Euclidean 3-dimensional space with a cross-cap singularity with respect to planes. This symmetry is picked up by the singularities of folding maps on the cross-cap. We give a list of the generic singularities that appear in the members of the family of folding maps on a cross-cap and characterise them geometrically.