The von Neumann ordinals are precisely the (wellfounded) hereditarily transitive sets. Does anyone on this list know who first proved it? Or who first published it? tf -- URL: www.dpmms.cam.ac.uk/~tf; DPMMS ph: +44-1223-337981; mobile in UK +44-7887-701-562; mobile in US: +1-412-818-1316; mobile in NZ +64-210580093.