A service subscription service business is a service provided to individuals and businesses that finds a lowest-cost provider or providers for subscription products and services as well as for one-time purchases of products and services. \u03b3,\u03b4-Unsaturated carboxylic acid derivatives are readily prepared through fewer steps and in high yields. Accordingly, at a position of a second substrate 2b corresponding to the region b, it is not necessary to provide a shading film 22. A second terminal link segment is formed by a terminal outer link member, one end of which is connected to a link pin.