All bridges consist of two main parts&colon; the substructure, and the superstructure. In Marxist theory, society consists of two parts&colon; the base (or substructure) and superstructure. It can be useful for constructing an elementary substructure of a large structure. Rotating a molecular substructure about a twistable bond usually requires energy. Population genetic substructure also can aid genetic association studies. Older Ionic temples normally lacked a specific visible substructure. Work on the bridge substructure (foundations) began in March 1973. The electron has no known substructure. The entrance into the substructure of the pyramid lay under the chapel's pavement. Conversely, the domain of an induced substructure is a closed subset. The substructure consisting of a nucleobase plus sugar is termed a nucleoside. However, there are several obvious ways to generalize notions such as substructure, homomorphism and identity. Construction commenced on the stadium substructure in October 2015. The older, inner pyramid is referred to as the "substructure". Substantial amounts of substructure are now expected.