A calculus for layered elastic media
, by Francis Muir & Joe Dellinger

Group theory provides a framework for deriving the properties of the homogeneous elastic
medium which is statically equivalent to a suite of anisotropic layers. Properties of a
layer map reversibly to an element of a commutative group, where adding elements gives the
group element for the homogeneous medium equivalent to the combination of two layers, and
subtravction corresponds to the removing of layers. Fractures are also representable as
group elements, allowing fractures and rocks to be manipulated together in a uniform manner.
A well-defined subgroup structure helps sort out the special properties of symmetry classes.