1.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.

1.这些许我们形式化反射的定义: 反射是欧里得空间的对等距同构，它的不动是余维度为 1 的仿射子空间。