I am looking for an word (adjective or noun) that describes the fact of two (or more) objects to be the same externally but different internally.
For example, how would you characterize the quality of two devices that perform the same function yet are intrinsically different when you examine them closer?
I am thinking of the word 'twin', but I am not completely satisfied with it. Any ideas?
This mechanical system can be in two different states, yet undistinguishable for an external observer. One can cause the system to switch between these _______ states by applying a certain force...