Regular green cities with two station slots (#14, #15) do not upgrade to brown. Regular green cities with one station slot (#12, #13, #205, #206) do.
Implementation Notes
Draft - the first player to have two shares of the L corporation becomes its president.
Nationalization - price is rounded up (i.e. stock price of 255 results in 383).
Quarry private companies may be sold between players only once per Stock Round - this condition is not enforced.
Presidency change - normally the new president decides the split - not implemented; they always give up two 10% shares (and keep a 20% share) if possible.
Mandatory investor exchange - if the associated corporation has not floated, the player receives the investor certificate anyway, but may not sell it before the company operates.
A corporation must own a train if it has a route. In the physical game, there are five 6+6. I decided to bump that quantity to nine in the implementation because it was technically possible to not have a train both in a corporation and in the supply.