Often people write these metrics as \(ds^2 = \sum_{i,j} g_{ij}\,dx^i\,dx^j\), where each \(dx^i\) is a covector (1-form), i.e. an element of the dual space \(T_p^*M\). For finite dimensional vectorspaces there is a canonical isomorphism between them and their dual: given the coordinate basis \(\bigl\{\frac{\partial}{\partial x^1},\dots,\frac{\partial}{\partial x^n}\bigr\}\) of \(T_pM\), there is a unique dual basis \(\{dx^1,\dots,dx^n\}\) of \(T_p^*M\) defined by \[dx^i\!\left(\frac{\partial}{\partial x^j}\right) = \delta^i{}_j.\] This extends to isomorphisms \(T_pM \to T_p^*M\). Under this identification, the bilinear form \(g_p\) on \(T_pM \times T_pM\) is represented by the symmetric tensor \(\sum_{i,j} g_{ij}\,dx^i \otimes dx^j\) acting on pairs of tangent vectors via \[\left(\sum_{i,j} g_{ij}\,dx^i\otimes dx^j\right)\!\!\left(\frac{\partial}{\partial x^k},\frac{\partial}{\partial x^l}\right) = g_{kl},\] which recovers exactly the inner products \(g_p\!\left(\frac{\partial}{\partial x^k},\frac{\partial}{\partial x^l}\right)\) from before. So both descriptions carry identical information;
到工程验收环节，验收人员通常只看“无障碍设施是否存在”，不细致测量是否符合国家标准、评估设施的便利性。验收时，绝大多数工程都缺少无障碍设施使用群体的实地体验，难以发现实际使用中的问题。根据2025年9月公布的“山东省临沂市罗庄区人民检察院督促城市公园无障碍设施规范建设行政公益诉讼案”，临沂市双月湖公园在未完成竣工验收的情况下向公众开放，结果发现，园内存在11处高差未设坡道、6座桥梁坡度过陡而无扶手、多处台阶过高等不符合国标的问题。
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孙氏三兄弟提起137件行政争议再审申请，就是一例。
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But vendors on eBay don't always pay attention. My Iwill XA100 motherboard uses 40-pins cable connectors so I explicitly ordered these. What ended up delivered were unfortunately 39-pin cables. Why oh why did manufacturers block that pin? Perhaps to prevent the ribbon from being connected the wrong way? But there was already a knot for that. The mystery lives on.