subspace

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式化反的定义: 反是欧几里得空间的对合等距同构，它的不动点集合是余维度为 1 的空间。