The no-hair theorem is the proposition that a black hole's state consists only of its mass, rotation, and electric charge (other than its position, velocity, and the attitude of its rotation axis), with no other qualities independent of these. The word hair is used metaphorically for any other qualities. A proof of the proposition would rest on the correctness of a good bit of physics, e.g., it might follow from general relativity, but proofs only of some black hole models have been accomplished. Its correctness is the conventional view of black holes but interest remains in proofs/disproofs/counter-examples. Data from GW detections are claimed to be consistent with the proposition. The implication of the theorem is that two black holes that are the same regarding those three values are identical, even, for example, if one was formed of matter and the other antimatter.