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).
A theoretical (or conceptual) definition is an abstract concept that defines a term in an academic discipline. Without a falsifiable operational definition, conceptual definitions assume both knowledge and acceptance of the theories that it depends on. A hypothetical construct may serve as a theoretical definition, as can a stipulative definition.