### a(n) is hmac-sha256(key=secret, data=a(n-1))
Courtesy of Verbatim
，这一点在PDF资料中也有详细论述
其一，国产创新药的发展，曾长期陷入“扎堆热门靶点”的内卷困境，PD-1等靶点动辄数十家企业布局，不仅造成研发资源的浪费，也使得产品缺乏差异化竞争力，难以诞生真正的大单品。
In Sweden, Synsam is one of the major Swedish retailers, as is the chain Synoptik. Some independent opticians also carry the glasses.