Observational Equivalence

This is the property of two or more entities to be indistinguishable based on their observable outputs.

• Internally, the systems could have different Models

Formal Definition

https://en.wikipedia.org/wiki/Observational_equivalence Two terms $M,N$ are observationally equivalent $⟺$ in all contexts, $C[\dots ]$, $C[M]=C[N]$ and $C[M]$. $C[N]$ are all valid terms.