李 “기름값 담합은 중대범죄…악덕기업, 대가 곧 알게될 것”
// `join!` runs both arms concurrently, but the `maybe` keyword means
，更多细节参见Feiyi
另外，西子健康营销投入的边际效益正呈现递减趋势。2024年及2025年前三季度，西子健康的销售费用增速分别是58.8%、31.2%，同期营收增速分别为16.9%、23.0%，公司营收增速显著低于销售费用增速，“烧钱换流量”的特征愈发明显。
Poincaré half-space model. Take the open upper half-space \[\mathbb{H}^n := \{(x_1,\dots,x_n)\in\mathbb{R}^n \mid x_n 0\}\] equipped with the Riemannian metric whose components on the coordinate tangent vectors are \[g_{ij}(p) \;=\; g_p\!\left(\frac{\partial}{\partial x_i}\bigg|_p,\; \frac{\partial}{\partial x_j}\bigg|_p\right) \;=\; \frac{1}{p_n^2}\,\delta_{ij}.\] Geodesics are semicircles (or rays) orthogonal to the boundary hyperplane \(\{x_n = 0\}\).