贝尔特拉米
In mathematics — specifically, in Riemannian geometry — Beltrami's theorem is a result named after the Italian mathematician Eugenio Beltrami which states that geodesic maps preserve the property of having constant curvature. More precisely, if ("M", "g") and ("N", "h") are two Riemannian manifolds and "φ" : "M" → "N" is a geodesic map between them, and if either of the manifolds ("M", "g") or ("N", "h") has constant curvature, then so does the other one.