-float norm(float x1, float y1, float x2, float y2);
-float pt_norm(point_t *p1, point_t *p2);
-float vect_norm(vect_t *v);
+float xy_norm(float x1, float y1, float x2, float y2);
+float pt_norm(const point_t *p1, const point_t *p2);
+float vect_norm(const vect_t *v);