# Y-Δ transform proof using superposition

In the wikipedia page and on every book they proof the transformation by equaling the the equivalent resistance between any pair of terminals while disconnecting the other node.https://en.wikipedia.org/wiki/Y-Δ_transform

Why this should make the two circuits equal? How can we apply superposition here? I have searched everywhere for this answer, In no where anyone explained this. Please explain the principle or this way of proof