// Sells owned shares of a defunct corporation, returning them to the
// corporation's stock
func (g *Game) sell(pl interfaces.Player, corp interfaces.Corporation, amount int) {
corp.AddStock(amount)
pl.RemoveShares(corp, amount).
AddCash(corp.StockPrice() * amount)
}
func (g *Game) buy(corp interfaces.Corporation, amount int) {
corp.RemoveStock(amount)
g.CurrentPlayer().
AddShares(corp, amount).
RemoveCash(corp.StockPrice() * amount)
}