  A theorem of Laman gives a combinatorial characterisation of the graphs that
admit a realisation as a minimally rigid generic bar-joint framework in
$\bR^2$. A more general theory is developed for frameworks in $\bR^3$ whose
vertices are constrained to move on a two-dimensional smooth submanifold $\M$.
Furthermore, when $\M$ is a union of concentric spheres, or a union of parallel
planes or a union of concentric cylinders, necessary and sufficient
combinatorial conditions are obtained for the minimal rigidity of generic
frameworks.
