Arlington County has an extensive network of bicycle infrastructure, including 50 miles of shared-use off-street trails. These multi-use trails are generally 10 feet wide with a solid yellow line striped down the middle to separate users.
Constructive mathematics. Idea. Broadly speaking, constructive mathematics is mathematics done without the principle of excluded middle (or other principles, such as the full axiom of choice, that imply it).
Constructive processes are processes that happen to the earth that build it up. One example of a constructive process is when sand is deposited on a river bank by the running water. The sand gathers, and builds the river bank up, making it higher. In the story, an example of a constructive process was the stalactites that grew from the deposition of the minerals.