In article <email@example.com>, david petry <firstname.lastname@example.org> wrote: >Any line segment joining two points reduces the >total number of degrees of freedom of the system of points and line >segments by one.
Not in general. Consider a deformable solid with a square face. Joining two opposite corners will make that square rigid. Joining the other two will have no further effect, while adding a line somewhere else in the solid may.