and Isaak Khalatnikov.

Superfluidity often co-occurs with Bose-Einstein condensation (BEC), but neither phenomenon is directly related to the other; not all Bose-Einstein condensates can be regarded as superfluids, and not all superfluids are Bose-Einstein condensates. Even when superfluidity and condensation co-occur, their magnitudes are not linked: at low temperature, liquid helium has a large superfluid fraction but a low condensate fraction;