These observations allow one to formalize the definition of reflection: a reflection is an involutive isometry of an Euclidean space whose set of fixed points is an affine subspace of codimension 1.

这些观察允许我们形射的定义: 射是欧几里得空间的对等距同构，它的不动点集是余维度为 1 的仿射子空间。