## 例文

- Let \ Delta be a triangle in X with geodesic segments as its sides . \ Delta is said to satisfy the \ mathbf { \ operatorname { \ textbf { CAT } } ( k ) } "'inequality "'if there is a
*comparison triangle*\ Delta'in the model space M _ k, with sides of the same length as the sides of \ Delta, such that distances between points on \ Delta are less than or equal to the distances between corresponding points on \ Delta '.