Geometric theory of hinged devices

This article contains results connected with engineering mechanics. Among them are: a theorem “on the nonuniqueness of a statically determinable truss”, a classification of hinged mechanisms and their schemes, and an example of a hinged mechanism with variable number of degrees of freedom. The study of general geometric properties is based on the concept, introduced here, of an abstract hinged device in $\mathbf R^d$. This concept formalizes a well-known approach in the theory of mechanisms. The formalization gives rise to a number of interesting mathematical questions.