Trade
every trade is fair. watch what happens anyway.
equal starts, fair coin-flip trades — one person ends up with everything
Every trade is a fair coin flip between equal parties, each staking a fair share of what they have. Run enough of them and wealth still concentrates toward one person holding it all, unless a small constant tax gives back what it takes.
Concepts: probability, inequality.
An interactive you play with one thumb, on Wundr.