Definitions
Isomorphic	Structures that are identical. For example, the special molds at the Billund factory ensure that each 2 × 2 Lego brick (Design ID 3003) is isomorphic
Isofunctional	Performing the identical function. For example, a pen, a pencil and a quill can all perform the same function
Heteromorphic	Structurally different elements. For example, a pen and a quill are heteromorphic
Degeneracy	The structural variation that underpins functional plasticity. For example, pens and pencils can perform the same function with respect to context. On earth, both pens and pencils can be used to write. Without structural modification, however, only pencils work in space